






















                                       SIO
                           Technical Reference Manual



                     Copyright (c) 1995 by Raymond L. Gwinn
                                26 Tanager Place
                          Beckley, West Virginia 25801
                               All Rights Reserved

                                 January 1, 1997


                             CompuServe: 72662,3547
                             InterNet: ray@gwinn.com
                              Voice: 1-304-255-7900
                               FAX: 1-303-255-7902
                     BBS: 1-304-255-7903 or vmbbs.gwinn.com
                            WEB http://www.gwinn.com






















                                  INTRODUCTION

     Documentation of software is often more difficult than writing the
     program itself (at least it is for this author).  I will do my best
     though.

     But who do I document for?  The user that is setting up a BBS just
     wants to get SIO installed and to move on to more important things. 
     The user that is having problems needs information about serial I/O
     communications in general and the PC specifically.  The application
     developer (programmer) needs detailed information about each
     individual function and the information generated.

     The answer is, more than one manual is needed.  This manual is
     intended as a reference for use by application programmers that
     desires to use SIO.  A separate Users Manual is included in the
     distribution file(s).

     This manual and the software described is provided as is and with no
     guarantees.  Use at your own risk.




     ii


     WHAT IS SIO . . . . . . . . . . . . . . . . . . . . . . . . . . .    1

     DISTRIBUTION, ORDERING AND SUPPORT  . . . . . . . . . . . . . . .    2
          Distribution and Ordering  . . . . . . . . . . . . . . . . .    2
               SIO Distribution and Support BBS  . . . . . . . . . . .    2
           . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .    2
               OS/2 Vendor Forum on
                    CompuServe . . . . . . . . . . . . . . . . . . . .    2
          Updates  . . . . . . . . . . . . . . . . . . . . . . . . . .    3

     Development and Debugging Tools . . . . . . . . . . . . . . . . .    4
          The Poor Man's Line Monitor (PMLM.EXE) . . . . . . . . . . .    4
          VIEWPMLM.EXE . . . . . . . . . . . . . . . . . . . . . . . .    5
          SIO's Utility (SU.EXE) . . . . . . . . . . . . . . . . . . .    5
               IRQs that currently free for use  . . . . . . . . . . .    5

     File System Requests  . . . . . . . . . . . . . . . . . . . . . .    6
          Driver Initialization  . . . . . . . . . . . . . . . . . . .    6
          Read . . . . . . . . . . . . . . . . . . . . . . . . . . . .    6
          Input Status . . . . . . . . . . . . . . . . . . . . . . . .    6
          Input Flush  . . . . . . . . . . . . . . . . . . . . . . . .    7
          Write  . . . . . . . . . . . . . . . . . . . . . . . . . . .    7
          Output Status  . . . . . . . . . . . . . . . . . . . . . . .    7
          Output Flush . . . . . . . . . . . . . . . . . . . . . . . .    7
          Open . . . . . . . . . . . . . . . . . . . . . . . . . . . .    7
               Initial Open  . . . . . . . . . . . . . . . . . . . . .    7
               Additional Open . . . . . . . . . . . . . . . . . . . .    8
          Close  . . . . . . . . . . . . . . . . . . . . . . . . . . .    8
               Intermediate Close  . . . . . . . . . . . . . . . . . .    8
               Last Close  . . . . . . . . . . . . . . . . . . . . . .    8

     Device I/O Control (IOCtl) Commands . . . . . . . . . . . . . . .    9
          IOCtl Functions From a DOS Session . . . . . . . . . . . . .   10
          41h - Set Bit Rate . . . . . . . . . . . . . . . . . . . . .   11
          42h - Set Line Characteristics . . . . . . . . . . . . . . .   12
          43h - Extended Set Bit Rate  . . . . . . . . . . . . . . . .   13
          44h - Transmit Byte Immediate  . . . . . . . . . . . . . . .   14
          45h - Set Break Off  . . . . . . . . . . . . . . . . . . . .   14
          46h - Set Modem Control Signals  . . . . . . . . . . . . . .   15
          47h - Hold Transmit  . . . . . . . . . . . . . . . . . . . .   16
          48h - Start Transmit . . . . . . . . . . . . . . . . . . . .   16
          4Bh - Set Break on . . . . . . . . . . . . . . . . . . . . .   17
          53h - Write Device Control Block (DCB)   . . . . . . . . . .   17
          54h - Write Extended Mode Parameters . . . . . . . . . . . .   20
          61h - Query Current Bit Rate . . . . . . . . . . . . . . . .   21
          62h - Query Line Characteristics . . . . . . . . . . . . . .   21
          63h - Query Extended Bit Rate  . . . . . . . . . . . . . . .   22
          64h - Query SIO Status . . . . . . . . . . . . . . . . . . .   23
          65h - Query Transmit Data Status . . . . . . . . . . . . . .   24
          66h - Query Current Modem Output Control Signals . . . . . .   25
          67h - Query Current Modem Input Signals  . . . . . . . . . .   25
          68h - Query Number of Characters in Receive Buffer . . . . .   26
          6Dh - Query SIO Error  . . . . . . . . . . . . . . . . . . .   27
          72h - Query SIO Event Information  . . . . . . . . . . . . .   28




                                                                        iii

          73h - Read Device Control Block (DCB)  . . . . . . . . . . .   29
          74h - Read Enhanced Mode Parameters  . . . . . . . . . . . .   29

     Differences between SIO/VSIO and COM/VCOM . . . . . . . . . . . .   30

     Appendix A, Hardware Port and IRQ Assignments . . . . . . . . . .   31
          Addresses and IRQs for COM1 and COM2 . . . . . . . . . . . .   31
          Defacto standard for COM3 and COM4 . . . . . . . . . . . . .   31
          Addresses and IRQ for COM3 through COM8 on the PS/2  . . . .   31

     Appendix B, SIO Chips . . . . . . . . . . . . . . . . . . . . . .   32
          8250 . . . . . . . . . . . . . . . . . . . . . . . . . . . .   32
          8250A  . . . . . . . . . . . . . . . . . . . . . . . . . . .   32
          16450  . . . . . . . . . . . . . . . . . . . . . . . . . . .   33
          16C451 . . . . . . . . . . . . . . . . . . . . . . . . . . .   33
          16550 (Non A)  . . . . . . . . . . . . . . . . . . . . . . .   33
          16550A . . . . . . . . . . . . . . . . . . . . . . . . . . .   33
          16550AF  . . . . . . . . . . . . . . . . . . . . . . . . . .   33
          16550AFN . . . . . . . . . . . . . . . . . . . . . . . . . .   33
          16550s Made by Western Digital . . . . . . . . . . . . . . .   34
          16C551 . . . . . . . . . . . . . . . . . . . . . . . . . . .   34
          16C552 . . . . . . . . . . . . . . . . . . . . . . . . . . .   34
          16C554 . . . . . . . . . . . . . . . . . . . . . . . . . . .   34
          82510  . . . . . . . . . . . . . . . . . . . . . . . . . . .   34
          16650  . . . . . . . . . . . . . . . . . . . . . . . . . . .   35
          16750 from Texas Instruments . . . . . . . . . . . . . . . .   35
          ComBic . . . . . . . . . . . . . . . . . . . . . . . . . . .   36

     Appendix C, Multi-Port Serial I/0 Cards . . . . . . . . . . . . .   37
          Hayes ESP  . . . . . . . . . . . . . . . . . . . . . . . . .   37
               ESP in Compatibility Mode . . . . . . . . . . . . . . .   37
          Telcor Tport . . . . . . . . . . . . . . . . . . . . . . . .   37

     . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .   38
          Gtek BBS550  . . . . . . . . . . . . . . . . . . . . . . . .   38
          Neotech Quad Serial (MCA bus)  . . . . . . . . . . . . . . .   39

     Appendix D, Advanced SIO Options  . . . . . . . . . . . . . . . .   40
          Protection . . . . . . . . . . . . . . . . . . . . . . . . .   40
          Locked Baud Rate . . . . . . . . . . . . . . . . . . . . . .   40
          IRQ Reflection to DOS Process  . . . . . . . . . . . . . . .   40
          I/O Port Mapping to DOS Process  . . . . . . . . . . . . . .   40

     Index . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .   41




                                                                          1

















                                   WHAT IS SIO

     SIO is a Serial Input/Output (SIO) communications character device
     driver.  It provides an interface between application programs and the
     serial communications hardware.

     SIO had been designed as a high performance replacement for the OS/2
     device driver COM.SYS.  This manual documents the known differences
     between COM.SYS and SIO.SYS.

     SIO only works with 8250 (type) serial I/O devices.  Such devices
     include, but is not limited to the 8250A, 16450, 16550, 16550A and the
     82510.  If you have a PC that is an IBM or near compatible which has a
     serial communication port, it is likely that it contains one of these
     devices.  SIO will identify the type of serial devices that it finds
     at load time.

     Like other Device Drivers, SIO will do very little standing alone. 
     There must be an application(s) program that makes use of SIO's
     functions before one will benefit from the use of SIO.




     2

                       DISTRIBUTION, ORDERING AND SUPPORT

     Distribution and Ordering

     The entire package collectively known as SIO is ShareWare.  It is not
     free software or freeware.  See LICENSE.TXT and ORDER.TXT for
     additional information.  The ShareWare version of SIO is distributed
     electronically.  One may check their favorite electronic hangout for
     the latest version of SIO.  The latest copy of the ShareWare version
     is always posted for downloading from the BBS at 1-304-255-7903 or
     vmbbs.gwinn.com and www.gwinn.com.

     Registered versions of SIO are distributed by US Mail and
     electronically from the SIO Distribution and Support BBS.  Users
     desiring to register electronically, may call the BBS and register on
     line (1-304-255-7903 or vmbbs.gwinn.com) and www.gwinn.com, and
     immediately download their registered version of SIO.  Use the ORDER
     command at the main BBS prompt.

     Registrations/Orders can also be placed by phone, mail, FAX, and
     email.  See the front cover of this manual for the phone numbers and
     addresses.  Also see ORDER.TXT for and order form that may be used.

     Support
     Extensive testing has been done to insure that this product works on
     the widest possible range of OS/2 V2 (and up) systems.  In most cases,
     problems can be resolved by reading this manual carefully.

     Support is provided in section 4 of the OS/2 Vendor Forum on
     CompuServe (GO OS2BVEN).  Section 4 of the OS2BVEN Forum is dedicated
     to the support of SIO.

     In addition, support is provided by BBS, Email and FAX.  Voice support
     would overwhelm the author and is not available.  If, after reading
     the manual carefully, you are unable to resolve a problem, you may
     submit a problem report to one of the following: 
                                      Email
                              CompuServe 72662,3547
                             Internet ray@gwinn.com
                               FAX 1-304-255-7902
                      BBS 1-304-255-7903 or vmbbs.gwinn.com

     Users should note that Support does not always result in a correction
     of a problem.  In addition, the support provided is support of SIO,
     and not the applications that use SIO.  Questions and/or problems
     about applications programs (such as terminal or FAX programs) should
     be directed to the available support for the application.




                                                                          3


     Updates

     In general, updates/upgrades of SIO are free of charge for all
     releases of SIO with the same major version number.  However, there
     may be a handling charge if the user requires the upgrade to be mailed
     or emailed.

     Registered users of SIO can update to the latest version FREE of
     charge using the BBS and its UPDATE command.  Be sure to have your SIO
     serial number when you first log onto the BBS.  All variations (number
     of ports) of SIO are available for immediate download from the BBS by
     registered users.

     Users that have a registered copy of SIO can also use REREG.EXE to
     transfer the registration information to a new version of SIO.  Simply
     unzip the new SIO files into a temporary directory, change to that
     directory, execute REREG and answer the questions.  After doing the
     above, all of the files in the temporary directory will have been
     registered.  You must then copy all the SYS and EXE files from the
     temporary directory to their normal directory (overlaying the old
     registered version) or execute the SIO install program (INSTALL.EXE). 
     Then you must reboot.  You may also want to check your CONFIG.SYS for
     the path of the SIO/VSIO being loaded and make sure both the new ones
     are being loaded.

     If REREG will not transfer your registration information from a
     previous version of SIO to the new version, then an upgrade must be
     ordered on disk or obtained from the support BBS.




     4

                         Development and Debugging Tools

     The Poor Man's Line Monitor (PMLM.EXE)

     PMLM is basically of interest to developers of comm applications and
     those providing technical support for those applications.  This SIO
     utility is released largely (in self defense) in the hope that some
     users can diagnose their own problems.  PMLM's feature of saving trace
     information to disk will only work with registered and beta versions
     of SIO.

     PMLM provides basic line monitoring for OS/2, DOS and Windows comm
     programs.  All characters sent or received by application programs are
     displayed in the upper portion of the screen.  Receive characters are
     displayed as "white on blue" and transmitted characters are displayed
     "yellow on violet".  Line signals, such as CTS are displayed as "dim
     white on red" when turned off and "bright white on red" when turned
     on.  In addition, a signals transition to OFF is displayed in lower
     case and a signals transition to ON is displayed in upper case.

     Status information is displayed in the lower part of the screen.  A
     bright white display means the signal is on, a dim white indicates
     that the signal is off.  In addition, when bright,  Rxoff and Txoff
     indicate the SIO has sent (Txoff) or received (Rxoff) an Xoff, and an
     Xon is pending.

     When a DOS or Windows session uses a comm port, an additional line of
     signal status appears.  This status line shows the state of the
     virtual UART's signals.  Only the signals which MAY be different from
     the real UART's signals are shown.

     "Rx Chars" and "Tx Chars" reflects the number of characters in SIO's
     receive and transmit buffers respectively.

     The last line on the screen shows the keys (from the keyboard) that
     PMLM will recognize.  The bright character shows the key to hit for
     the associated function.  The font keys will not work in a windowed
     OS/2 session.

     PMLM's command line requires one parameter, the comm port number, and
     optionally accepts an additional parameter giving a save trace file
     name.  For example, PMLM 1 COM1INFO.TEC will monitor COM1 and save ALL
     of the communications traffic in the file COM1INFO.TRC.  The trace
     files created by PMLM contain exactly the same information that is
     displayed by PMLM, video attributes and all.




                                                                          5


     VIEWPMLM.EXE may be used to view trace files created by PMLM. 
     VIEWPMLM.EXE requires one parameter, the trace file name.  The user
     can use the keys UP, DOWN, PAGEUP, PAGEDOWN, HOME, and END to navigate
     the saved trace file.  Registered SIO users may send VIEWPMLM.EXE
     (along with saved trace files) to anyone for technical support
     purposes.

     VIEWPMLM can be used in native DOS, in DOS sessions under OS/2, and in
     OS/2 sessions.  This means that even those developers and support
     people need not have OS/2 to view the captured communications data
     created by PMLM.

     SIO's Utility (SU.EXE)

     This utility program has several useful commands.  You can obtain a
     list of the available commands by typing SU at any command line prompt
     without any parameters.  One very useful command is SU IRQS.  This
     command will show IRQs that currently free for use.  Commands are
     provided allowing user control (missing from MODE) are available. 
     Status commands provide a wealth of diagnostic information.




     6

                              File System Requests

     SIO processes all file system requests made to it in one way or
     another.  The following file system requests and how SIO processes
     them may be of use to the application programmer.

     INIT           Driver initialization.
     Read           Data transfer from driver to program.
     Input Status   Get input status.
     Input Flush    Terminate all pending input requests.
     Write          Data transfer from program to driver.
     Output Status  Get output status.
     Output Flush   Terminate all pending output requests.
     Open           Open the device for use.
     Close          Close the device.
     IOCTL          Device I/O control commands.

     Each of these file system requests are discussed in more detail in the
     following.

                              Driver Initialization

     During device driver initialization the command line is parsed, memory
     for data and control buffers is allocated and the system environment
     is examined.

     Buffers are allocated for the maximum number of ports that the
     installed version of SIO can support (up to 16).

     The mouse port is determined and if it is a serial mouse, that port is
     excluded from use by SIO.

     In the absence of any command line parameters, SIO will only support
     (look for) COM1 and COM2 at the standard addresses.  COM3 and up will
     not be supported (or looked at) unless they are specifically
     identified in the SIO command line.

                                      Read

     If another read is already in progress, the process issuing the
     additional read is blocked (suspended) until the previous read command
     completes.  When a read is started, that read is not interrupted by
     additional reads.  If multiple reads are issued, they are not
     necessarily processed in the order they were issued.  Thus,
     applications may not see the read requests complete in the order in
     which they were issued.

     The conditions that control when the read will complete are controlled
     by the active (current) DCB when the read is started.

                                  Input Status

     This function returns with "device busy" set if there is no data in
     the receive buffer.  That is, busy is returned if the process may be
     blocked if the application issues a read command.




                                                                          7

                                   Input Flush

     This function causes the receive buffer to be cleared (made empty). 
     Any threads that are blocked, waiting for a read, will be restarted
     when this function is issued.


                                      Write

     If another write is already in progress, the process issuing the
     additional write is blocked (suspended) until the previous write
     command completes.  When a write is started, that write is not
     interrupted by additional writes.  If multiple writes are issued, they
     are not necessarily processed in the order they were issued.  Thus,
     applications may not see the write requests complete in the order in
     which they were issued.

     The conditions that control when the write will complete are
     controlled by the current DCB when the write is started.


                                  Output Status

     This function returns with "device busy" set if the output buffer is
     more than three quarters full.  That is, busy is returned if the
     process may be blocked if the application issues a write command.

                                  Output Flush

     This function causes the transmit buffer to be cleared (made empty). 
     Any threads that are blocked, waiting for a write, will be restarted
     when this function is issued.


                                      Open

     There are basically two kinds of open.  They are an Initial Open and
     Additional (shared) Opens. The IBM documentation calls the initial
     open a First Level Open.  An Initial Open is an open that occurs when
     no other process has the communications port open.  An Additional Open
     is when an open occurs and another process already has the
     communications port open.  For an Additional Open to occur, the
     Initial Opener must have issued an open allowing shared access to the
     port.

     Initial Open

     The IRQ associated with the comm port is claimed (taken) when the
     Initial Open occurs.  If the associated IRQ is not available a "Port
     in Use" error is returned.  At the time of this writing, the IRQ is
     claimed allowing sharing.  However, the shared IRQ claiming is done to
     circumvent anomalies in the OS, and in actuality SIO will not
     concurrently share an IRQ with another device driver.  The author
     found it necessary to claim (reset) all interrupts directed to the
     interrupt service routine in order to prevent lock ups of a




     8

     communications port.  The IRQ mess may be cleaned up at a future date
     when the OS problems are corrected.

     During Initial Opens, DTR and RTS are set in accordance with the
     current Device Control Block (DCB) settings.  If DTR Control Mode is
     the "Enabled" option ( bits 1 and 0 of the DCB Flags1 byte equal 01),
     then DTR is turned on.  Otherwise, DTR is unchanged by the Initial
     Open.  Similarly, if RTS Control Mode is the "Enabled" option ( bits 7
     and 6 of the DCB Flags1 byte equal 01), then RTS is turned on. 
     Otherwise, RTS is unchanged by the Initial Open.

     The following actions also occur during an Initial Open:

          The Xon and Xoff characters are set to 11h and 13h respectively.

          The transmit and receive buffers and structures are cleared and
          re-initialized.

          Status bits are reset.

     If the Initial Opener is an OS/2 process (not a DOS process) then the
     Read time out processing is set to "Normal" in the current DCB.

     Additional Open

     A count of active opens is incremented.  No changes are made to
     current comm settings.

                                      Close

     There are two basic kinds of closes.  They are an Intermediate Close
     and a Last Close.

     Intermediate Close

     An intermediate close occurs when a process issues a close and other
     processes still have the communications port opened.  This type of
     close simply decrements an open count and returns.  No action or
     changes take place at the communications port.

     Last Close

     The last close occurs when a process issues a close and no other
     process has the communications port open.  If there are any writes
     pending or incomplete, the process is blocked (suspended) until the
     writes complete or time out.  If 60 seconds pass with no activity at
     the communications port, the port is forced to close and all writes
     are terminated.  If any processes are blocked (suspended) waiting on a
     read, they are forced to return to the process that issued the read.

     If either DTR Control Mode or RTS Control Mode are set to "Enabled" by
     the current DCB, then the appropriate signal(s) is turned off.

     Finally, the IRQ is released back to the OS.




                                                                          9

                       Device I/O Control (IOCtl) Commands

     The following Generic IOCtl functions are supported by SIO.
          41h - Set Bit Rate
          42h - Set Line Characteristics
          43h - Extended Set Bit Rate
          44h - Transmit Byte Immediate
          45h - Set Break Off
          46h - Set Modem Control Signals
          47h - Hold Transmit
          48h - Start Transmit (after hold)
          4Bh - Set Break On
          53h - Write Device Control Block (DCB) 
          54h - Write Extended Mode Parameters
          61h - Query Current Bit Rate
          62h - Query Line Characteristics
          63h - Query Extended Bit Rate
          64h - Query SIO Status
          65h - Query Transmit Data Status
          66h - Query Current Modem Output Control Signals
          67h - Query Current Modem Input Signals
          68h - Query Number of Characters in Receive Buffer
          69h - Query Number of Characters in Transmit Buffer
          6Dh - Query SIO Error
          72h - Query SIO Event Information
          73h - Read Device Control Block (DCB)
          74h - Read Enhanced Mode Parameters

     Each of these IOCtl commands are described in detail on the following
     pages.




     10


     All IOCtl functions are called with a uniform set of parameters.  This
     uniform set of parameters is:
          DWORD     Address of a data packet.
          WORD      Size of the data packet in bytes.
          DWORD     Address of the parameter packet.
          WORD      Size of the parameter packet in bytes.
          WORD      Function code.
          WORD      Category code (01 for SIO).
          WORD      Handle for the opened device. 

     Each IOCtl function may or may not have a data or parameter packet. 
     If a given IOCtl function specifies a NULL parameter or data packet,
     the address of the appropriate item must be NULL (zero) in the
     parameters.  Passing an invalid data or parameter packet may result in
     a General Protection Fault.

     IOCtl Functions From a DOS Session

     Additionally the following describes how to call an IOCtl function in
     an OS/2 driver from a DOS session (VDM).  The "handle" is obtained
     simply by issuing a normal DOS open of the device, ie COM1.  The Data
     Packets (DataPkt below) and Parameter Packets (PrmPkt below) are
     different for each IOCtl function.  The structure and contents of
     these packets are described in the following pages.

             push    ds              ;save ds
             mov     bx,handle       ;file handle to bx
             mov     ch,1            ;category, 1=serial device control
             mov     cl,41h          ;func code, 41h=extended set bit rate
             mov     dx,Seg DataPkt  ;get segment of the data packet
             mov     ds,dx           ;load ds with seg of the data packet
             lea     dx,DataPkt      ;data packet address to ds:dx
             mov     si,Seg PrmPkt   ;segment of command packet to si
             lea     di,PrmPkt       ;offset of command packet to di
             mov     ax,440ch        ;IOCtl function call, handle based
             int     21h             ;issue IOCtl to OS/2 driver.
             pop     ds              ;restore ds
             jc      error           ;jump if error returned




                                                                         11


                               41h - Set Bit Rate

     Parameter Packet

          Ŀ
                   Item                Type     
          Ĵ
           Bit/Baud Rate              WORD     
          

          "Bit Rate" is any number from 1 to 65535.  SIO does not attempt
          to validate a given bit rate.  The minimum bit rate accepted by
          SIO is 50, the maximum for this IOCtl function is 65535.

          Note that the hardware may not be able to generate the given bit
          rate.  For example, if a computer has a standard communications
          card installed and if a bit rate of 65500 is specified, the
          nearest bit rate that can be generated will be set, 57600 in this
          case.

          To set bit rates in excess of 57600, see IOCtl function 43h,
          Extended Set Bit Rate.

          Some commonly used bit rates that can be set with this function
          are:

          50        2000
          75        2400
          110       3600
          150       4800
          300       7200
          600       9600
          1200      19200
          1800      28800
          2000      38400
          2400      57600


     Data Packet - None




     12


                         42h - Set Line Characteristics

     Parameter Packet

          Ŀ
                   Item                Type     
          Ĵ
           Data Bits Per Character    BYTE     
          Ĵ
           Parity Setting             BYTE     
          Ĵ
           Stop Bit Setting           BYTE     
          

          Data Bits Per Character may be 5, 7, or 8, all other values are
          invalid.

          Parity Setting may have the following values, all other values
          are invalid:
               0 - No parity bit.
               1 - Odd parity.
               2 - Even parity.
               3 - Mark parity (1).
               4 - Space parity (0).


          Stop Bit Setting may have the following values, all other values
          are invalid:
               0 - 1 stop bit.
               1 - 1.5 stop bit (valid with 5 data bit characters).
               2 - 2 stop bits.


     Data Packet - None




                                                                         13


                           43h - Extended Set Bit Rate

     Parameter Packet

          Ŀ
                   Item                Type     
          Ĵ
           Bit/Baud Rate              DWORD    
          Ĵ
           Fraction                   BYTE     
          


          "Bit Rate" is the desired bit/baud rate.  The maximum bit rate
          supported by SIO is determined by the installed hardware. The
          IOCtl function "63h - Query Extended Bit Rate" can be used to
          determine the maximum bit rate allowed for the associated
          hardware.

          SIO does not attempt to validate a given bit rate.  This means
          that the hardware may not be able to generate the given bit rate. 
          For example, if a computer has a standard communications card
          installed and if a bit rate of 65500 is specified, the nearest
          bit rate that can be generated will be set, 57600 in this case.

          "Fraction" is used to set the fractional part of the bit rate
          when a high degree of accuracy is needed.  As of this writing,
          SIO does not support a "Fraction" other than zero.

          Some commonly used bit rates that can be set with this function
          are:

          110       3600      115200
          150       4800      230400
          300       7200      460800
          600       9600      921600
          1200      19200
          1800      28800
          2000      38400
          2400      57600

     Data Packet - None




     14


                          44h - Transmit Byte Immediate

     Parameter Packet

          Ŀ
                   Item                Type     
          Ĵ
           Character to Transmit      BYTE     
          

          "Character to Transmit" will be the next character loaded into
          the UART for transmission.  If a previous transmit immediate byte
          is still pending, it is lost.  This function does not wait for
          the character to transmit before returning.

          This function may be used by an application program as one of a
          set of functions to implement its own Xon/Xoff type handshaking.

     Data Packet - None


                               45h - Set Break Off

     Parameter Packet - None

          Look!! No Parameter Packet!

     Data Packet

          Ŀ
                   Item                Type     
          Ĵ
           SIO Error Word             WORD     
          

          See function 6Dh "Query SIO Error" for a description of the SIO
          Error Word.  This function does not reset any bits in the SIO
          Error Word.




                                                                         15


                         46h - Set Modem Control Signals

     Parameter Packet

          Ŀ
                   Item                Type     
          Ĵ
           DTR and RTS on mask        BYTE     
          Ĵ
           DTR and RTS off mask       BYTE     
          

          Attempted changes in the the setting of signals that are used as
          flow control signals are ignored.  The current DCB determines if
          either or both RTS and DTR are used as a flow control signal.

          The setting of bit 0 affects DTR and the setting of bit 1 affects
          RTS.  Ones in the "on mask" specifies which of the two signals
          are to be turned on, and zeros in the "off mask" specify which of
          the two signals are to be turned off.

          Some examples are:
               On Mask        Off Mask
               01h            0FFh      Turn DTR on
               00h            0FEh      Turn DTR off
               02h            0FFh      Turn RTS on
               00h            0FDh      Turn RTS off
               03h            0FFh      Turn RTS and DTR on
               00h            0FCh      Turn RTS and DTR off

          If both on and off are specified for the setting of a signal, the
          result is undefined.

     Data Packet

          Ŀ
                   Item                Type     
          Ĵ
           SIO Error Word             WORD     
          

          See function 6Dh "Query SIO Error" for a description of the SIO
          Error Word.  This function does not reset any bits in the SIO
          Error Word.




     16


                               47h - Hold Transmit

     Parameter Packet - None

     Data Packet - None

          This function will disable the transmitter.  The transmitter will
          not be enabled again unless IOCtl function 48h is issued.  If the
          transmitter is already disabled, this call has no effect.

          This function can be used as part of a set that allows an
          application to implement its own Xon/Xoff type handshaking.

          Note that this is different from how COM.SYS implements this
          function.  COM.SYS will re-enable the transmitter if an Xon is
          received while SIO will not.


                              48h - Start Transmit

     Parameter Packet - None

     Data Packet - None

          This function will enable the transmitter, usually following an
          IOCtl function 47h.  If the transmitter is already enabled, this
          call has no effect.

          This function can be used as part of a set that allows an
          application to implement its own Xon/Xoff type handshaking.




                                                                         17


                               4Bh - Set Break on

     Parameter Packet - None

          Look!! No Parameter Packet!

     Data Packet

          Ŀ
                   Item                Type     
          Ĵ
           SIO Error Word             WORD     
          

          See function 6Dh "Query SIO Error" for a description of the SIO
          Error Word.  This function does not reset any bits in the SIO
          Error Word.


                     53h - Write Device Control Block (DCB) 

     This is where the action is!  See also function 73h (Read DCB).

     Parameter Packet

          Ŀ
                   Item                Type     
          Ĵ
           Write Timeout              WORD     
          Ĵ
           Read Timeout               WORD     
          Ĵ
           Flags1                     BYTE     
          Ĵ
           Flags2                     BYTE     
          Ĵ
           Flags3                     BYTE     
          Ĵ
           Error Replacement Byte     BYTE     
          Ĵ
           Break Replacement Byte     BYTE     
          Ĵ
           Xon Character              BYTE     
          Ĵ
           Xoff Character             BYTE     
          


          "Write Timeout"  The write timeout is given in hundredths of a
          second, relative to zero.  That is, 0 specifies 0.01 seconds and
          1 specifies 0.02 seconds.

          "Read Timeout" The read timeout is given in hundredths of a
          second, relative to zero.  That is, 0 specifies 0.01 seconds and




     18

          1 specifies 0.02 seconds.

          "Flags1" is a bit flag.  The bits in the flag specify the
          following:

          Bits 1 and 0        DTR Control Mode.
                    00 - Disable changing DTR during Open and Close.
                    01 - Enable Changing DTR during Open and Close.
                    10 - DTR used for input handshaking (not supported by
                         SIO).
                    11 - Invalid

          Bit 2,    Must be zero
          Bit 3,    Off to ignore CTS.  Forced on if RTS is handshake.
          Bit 4,    DSR is handshake.  Not supported by SIO.
          Bit 5,    DCD required to transmit.  Not supported by SIO.
          Bit 6,    DSR required to receive.
          Bit 7,    Must be zero.

     

          "Flags2" is a bit flag.  The bits in the flag specify the
          following:

          Bit 0,    SIO is to honor Xon/XOff received from remote.
          Bit 1,    SIO may send Xon/Xoff to the remote.
          Bit 2,    Enable error replacement character.  Not supported by
                    SIO.

          Bit 3,    Enable null stripping.  Not supported by SIO.
          Bit 4,    Enable break replacement character.  Not supported by
                    SIO.

          Bit 5,    Enable Full duplex.  Half duplex is not supported by
                    SIO.

          Bits 7 and 6        RTS Control Mode
                    00 - Disable changing RTS during Open and Close.
                    01 - Enable Changing RTS during Open and Close.
                    10 - RTS used for input handshaking.
                    11 - Toggle on transmit (half duplex).  Not supported
                         by SIO.




                                                                         19

          "Flags3" is a bit flag.  The bits in the flag specify the
          following:

          Bit 0,    Enable infinite write timeout processing.  When set, a
                    write timeout will not occur.

          Bits 2 and 1        Read timeout processing
                    00 - Invalid.
                    01 - Normal read time out.
                    10 - Wait for something.  Reads will return before a
                         timeout occurs if something received.
                    11 - No Wait.  Reads will return immediately with any
                         available data.

          Bits 4 and 3        FIFO Control
                    00 - No change in FIFO state.
                    01 - Disable FIFO buffers.
                    10 - Enable FIFO buffers.
                    11 - Dynamic enabling and disabling of FIFOS.

               **Note, SIO forces bits 4 and 3 to "10".

          Bits 6 and 5        Set receive trigger level
                    00 - 1 character.
                    01 - 4 characters.
                    10 - 8 characters.
                    11 - 14 characters.

               **Note, SIO forces bits 6 and 5 to "10".

          Bit 7               Transmit load count
                    0 -  Load 1 character.
                    1 -  Load 16 characters.

               **Note, SIO forces bit 7 to "1".

          "Error Replacement Byte" Not supported by SIO.

          "Break Replacement Byte" Not supported by SIO

          "Xon Character" Any value, default is 11h.

          "Xoff Character" Any value, default is 13h.

     Data Packet - None




     20


                      54h - Write Extended Mode Parameters

     Parameter Packet

          Ŀ
                   Item                Type     
          Ĵ
           Enhanced Flags1            BYTE     
          Ĵ
           Reserved                   DWORD    
          

          This function is not supported (ignored) by SIO.  However the
          bits are defined here for completeness.

          Enhanced Flags1
          Bit 0 -   Enhanced mode hardware available (Query only 74h).
          Bit 1 -   Enable enhanced mode.
          Bits 3 and 2        DMA Receive Operation
               00 - Disable DMA receive capability.
               01 - Enable DMA receive capability.
               10 - Dedicate a DMA channel to receive.
               11 - Reserved.

          Bits 5 and 4        DMA Transmit Operation
               00 - Disable DMA transmit capability.
               01 - Enable DMA transmit capability
               10 - Dedicate a DMA channel to transmit.
               11 - Reserved.

          Bit 6 -   Receive in DMA mode (Query only, 74h).
          Bit 7 -   Transmit in DMA mode (Query only, 74h).

     Data Packet - None.




                                                                         21


                          61h - Query Current Bit Rate

     Parameter Packet - None.

     Data Packet

          Ŀ
                   Item                Type     
          Ĵ
           Bit/Baud Rate              WORD     
          

          See function 41h for more information.


                        62h - Query Line Characteristics

     Parameter Packet - None.


     Data Packet


          Ŀ
                   Item                Type     
          Ĵ
           Data Bits Per Character    BYTE     
          Ĵ
           Parity Setting             BYTE     
          Ĵ
           Stop Bit Setting           BYTE     
          Ĵ
           Transmitting Break         BYTE     
          

          See function 42h for a definition of Data, Parity and Stop Bits.

          "Transmitting Break" is set to 1 if a break is being transmitted. 
          Otherwise, it is set to zero.




     22


                          63h - Query Extended Bit Rate

     Parameter Packet - None


     Data Packet

          Ŀ
                   Item                Type     
          Ĵ
           Current Bit/Baud Rate      DWORD    
          Ĵ
           Fraction of Current        BYTE     
          Ĵ
           Minimum Bit/Baud Rate      DWORD    
          Ĵ
           Fraction of Minimum        BYTE     
          Ĵ
           Maximum Bit/Baud Rate      DWORD    
          Ĵ
           Fraction of Maximum        BYTE     
          

          "Current Bit/Baud Rate" is a 32 bit integer defining the current
          bit rate.

          "Fraction of Current" is always 0 when returned by SIO.

          "Minimum Bit/Baud Rate" is the minimum value that can be passed
          to SIO as a bit/baud rate.

          "Fraction of Minimum" is always 0 when returned by SIO. 

          "Maximum Bit/Baud Rate" is the maximum value that can be passed
          to SIO as a bit/baud rate.

          "Fraction of Maximum" is always 0 when returned by SIO.




                                                                         23


                             64h - Query SIO Status

     Parameter Packet - None

     Data Packet

          Ŀ
                   Item                Type     
          Ĵ
           SIO Status Byte            BYTE     
          

          "SIO Status Byte" is a bit flag.  The bits have the following
          meanings:

          Bit 0 -   Set if SIO is waiting for CTS before transmitting.
          Bit 1 -   Set if SIO is waiting for DSR before transmitting.
          Bit 2 -   Set if SIO is waiting for DCD before transmitting.
          Bit 3 -   Set if SIO is waiting because Xoff received or
                    transmitter is disabled (see function 47h).

          Bit 4 -   Reserved, not used by SIO.
          Bit 5 -   Set if SIO is waiting because break is being sent.
          Bit 6 -   Set if a transmit immediate is pending.
          Bit 7 -   Reserved, not used by SIO.




     24


                        65h - Query Transmit Data Status

     Parameter Packet - None.

     Data Packet

          Ŀ
                   Item                Type     
          Ĵ
           Transmit Status            BYTE     
          

          "SIO Status Byte" is a bit flag.  The bits have the following
          meanings:

          Bit 0 -   Set if write in progress or pending.
          Bit 1 -   Set if any data is in the transmit buffer.
          Bit 2 -   Set if UART is currently transmitting.
          Bit 3 -   Set if a transmit immediate is pending.
          Bit 4 -   Set if an Xon needs to be sent.
          Bit 5 -   Set if an Xoff needs to be sent.
          Bit 6 -   Reserved
          Bit 7 -   Reserved




                                                                         25


                66h - Query Current Modem Output Control Signals


     Parameter Packet - None.

     Data Packet

          Ŀ
                   Item                Type     
          Ĵ
           Modem Output Signals       BYTE     
          

          "Modem Output Signals" is a bit flag.  The bits have the
          following meanings:

          Bit 0 -   Set if DTR is currently on.
          Bit 1 -   Set if RTS is currently on.
          Bits 2-7  Reserved, set to zero by SIO.


                     67h - Query Current Modem Input Signals

     Parameter Packet - None.

     Data Packet

          Ŀ
                   Item                Type     
          Ĵ
           Modem Input Signals        BYTE     
          

          "Modem Output Signals" is a bit flag.  The bits have the
          following meanings:

          Bits 0-3  Reserved, set to zero by SIO.
          Bit 4 -   Clear To Send (CTS) is active.
          Bit 5 -   Data Set Ready (DSR) is active.
          Bit 6 -   Ring Indicator (RI), trailing edge detected.
          Bit 7 -   Data Carrier Detect (DCD) is active.




     26


               68h - Query Number of Characters in Receive Buffer

     Parameter Packet - None.

     Data Packet

          Ŀ
                   Item                Type     
          Ĵ
           Number of Bytes Buffered   WORD     
          Ĵ
           Byte Size of the Buffer    WORD     
          

          Self explaining.


               69h - Query Number of Characters in Transmit Buffer

     Parameter Packet - None.

     Data Packet

          Ŀ
                   Item                Type     
          Ĵ
           Number of Bytes Buffered   WORD     
          Ĵ
           Byte Size of the Buffer    WORD     
          

          Self explaining.




                                                                         27


                              6Dh - Query SIO Error


     Parameter Packet - None.

     Data Packet

          Ŀ
                   Item                Type     
          Ĵ
           SIO Error Word             WORD     
          

          "SIO Error Word" is a bit flag.  The bits have the following
          meaning:

          Bit 0 -   Set if a buffer overrun has occurred.
          Bit 1 -   Set if an overrun occurred at the UART.
          Bit 2 -   Set if the UART detected a parity error.
          Bit 3 -   Set if the UART detected a framing error.
          Bits 4-15 Reserved, set to zero by SIO.

          All bits of the SIO Error Word are reset prior to returning to
          the caller.




     28


                        72h - Query SIO Event Information

     Parameter Packet - None.

     Data Packet

          Ŀ
                   Item                Type     
          Ĵ
           SIO Event Word             WORD     
          

          "SIO Event Word" is a bit flag.  The bits have the following
          meaning:

          Bit 0 -   Set when a receive character is transferred from the
                    UART to the receive buffer.
          Bit 1 -   Set when a receive (Read) timeout occurs.
          Bit 2 -   Set if the transmit buffer is empty.
          Bit 3 -   Set if Clear To Send (CTS) has changed state.
          Bit 4 -   Set if Data Set Ready (DSR) has changed state.
          Bit 5 -   Set if Data Carrier Detect (DCD) has changed state.
          Bit 6 -   Set if a break has been detected.
          Bit 7 -   Set if a framing, parity, or overrun error has
                    occurred.
          Bit 8 -   Set if trailing edge of Ring Indicator (RI) has
                    occurred.
          Bits 9-15 Reserved, set to zero by SIO.

          All bits are reset prior to returning to the caller.




                                                                         29


                      73h - Read Device Control Block (DCB)

     Parameter Packet - None.


     Data Packet

          Ŀ
                   Item                Type     
          Ĵ
           Write Timeout              WORD     
          Ĵ
           Read Timeout               WORD     
          Ĵ
           Flags1                     BYTE     
          Ĵ
           Flags2                     BYTE     
          Ĵ
           Flags3                     BYTE     
          Ĵ
           Error Replacement Byte     BYTE     
          Ĵ
           Break Replacement Byte     BYTE     
          Ĵ
           Xon Character              BYTE     
          Ĵ
           Xoff Character             BYTE     
          

          See function 53h for a description of the parameters.


                       74h - Read Enhanced Mode Parameters

     Parameter Packet - None.

     Data Packet

          Ŀ
                   Item                Type     
          Ĵ
           Enhanced Flags1            BYTE     
          Ĵ
           Reserved                   DWORD    
          

          See function 54h for a description of the Flags1 Byte.




     30

                    Differences between SIO/VSIO and COM/VCOM
     What follows is some of the differences between SIO/VSIO and COM/VCOM
     that are known to the author.

     1 -  COM.SYS will automatically seek out and support four comm
          ports, COM1 through COM4.  SIO.SYS will automatically seek
          out and support only COM1 and COM2.  If SIO.SYS is to
          support more than two comm ports, they must be defined in
          the command line that loads SIO.SYS.  For example,
          DEVICE=SIO.SYS (COM3) (COM4) will cause SIO.SYS to support
          four comm ports.

     2 -  In the absence of overrides in the command line, COM.SYS
          will seek out four comm ports in the sequence of I/O ports
          3F8h, 2F8h, 3E8h and 2E8h.  The first port found in this
          sequence is given the logical name COM1, the second is COM2
          etc.  This means that the comm port at 2F8h could become
          COM1.  In the opinion of the author, this confuses some
          users to frustration.

          With no command line overrides, SIO.SYS uses a fixed I/O
          port concept.  That is, COM1 is always at I/O port 3F8h,
          COM2 is always at 2F8h, etc.  Another way of looking at this
          is;  if no comm port exists at port 3F8h, then you do not
          have a COM1.  SIO.SYS will not move another (found) comm
          port into the logical COM1 slot.

     3 -  VSIO opens a comm port for a DOS session with sharing allowed. 
          VCOM uses an "exclusive use" open for DOS sessions.

     4 -  SIO.SYS will accept any number from 50 up as a valid baud rate. 
          For example, if an application program attempts to set a baud
          rate of 9990 bps, COM.SYS will reject it and SIO.SYS will accept
          it.

     5 -  SIO/VSIO execute faster than COM/VCOM.  This means that some
          applications, that are timing dependent, may not work under
          SIO/VSIO that do work under COM/VCOM.

     6 -  SIO/VSIO provides more reliable active flow control for DOS
          sessions.  For example, if RTS/CTS handshaking is in use, VSIO
          virtualizes the RTS settings by the DOS program while SIO
          completely controls the real RTS signal.  COM/VCOM simply passes
          the RTS signal directly to the hardware.

     7 -  COM.SYS will block an application until a write completes.  SIO
          will return to the application program immediately if all of the
          write data will fit into SIO's internal buffers.




                                                                         31

                  Appendix A, Hardware Port and IRQ Assignments

     I have obtained the following information from various sources. 
     Accuracy is not guaranteed.  In fact, nothing in this document is
     guaranteed.

     Addresses and IRQs for COM1 and COM2

          COM1 uses 03F8h and IRQ4
          COM2 uses 02F8h and IRQ3

     Defacto standard for COM3 and COM4 for PC, XT and AT

          COM3 uses 03E8h and IRQ4
          COM4 uses 02E8h and IRQ3

     Addresses and IRQ for COM3 through COM8 on the PS/2

          COM3 uses 3220h and IRQ3
          COM4 uses 3228h and IRQ3
          COM5 uses 4220h and IRQ3
          COM6 uses 4228h and IRQ3
          COM7 uses 5220h and IRQ3
          COM8 uses 5228h and IRQ3

     All PCs (known to the author) prior to the PS/2 and EISA only use 10
     bits to address hardware I/0 ports.  Systems prior to the PS/2 and
     EISA can not address the standard PS/2 addresses for COM3 through
     COM8.  If an AT or below attempts to address COM3 through COM8 using
     the PS/2 addresses, only the low 10 bits of the address are used. 
     That is, the high 6 bits of the address will be ignored by the
     hardware.  This means that any reference to COM3 through COM8 will
     actually address ports 220h through 22Fh on older PCs.

     One should avoid expansion boards that use ports 220h through 22Fh
     unless the expansion board is a serial I/O board. 

     SIO will (attempt to) determine the hardware architecture (ISA/EISA
     and PS/2) that it is being executed on and use the appropriate
     hardware port addresses for COM1 thru COM4 as defaults.




     32

                              Appendix B, SIO Chips


     The following is a collection of comments developed from hearsay,
     random documents, experience, and technical specifications. So, take
     it with a grain of salt.  Order information from the various
     manufactures if you want accurate information.

     Very good reference books are available from National Semiconductor
     Corporation.  They cover most of the SIO devices (also called UARTs)
     that you will find in many PCs and clones.  I am not sure that books
     can be ordered directly from National Semiconductor. They may require
     that you get it from a distributor.  In any case, the address on the
     back of the one manual is:

          National Semiconductor Corporation
          2900 Semiconductor Drive
          P.O. Box 58090
          Santa Clara, CA 95052-8090

          Tel:(408)721-5000
          TWX:(910)339-9240

     8250

     As best I known, the 8250 was the first SIO chip (integrated circuit)
     that was used by the IBM PC and many clones.  In my opinion, it was a
     poor choice on the part of IBM.  I feel many superior devices, at
     comparable prices, were readily available.  At that time, I feel the
     8251A or the 8530 would have been better choices.  But, they used the
     8250 and therefore we must use it.

     From a hardware standpoint the 8250 is a relatively slow device.  It
     is advisable that programmers not perform successive inputs or outputs
     to this device.  It seems that software programs can load the various
     registers of the 8250 faster than it can process the information.  The
     8250 had a total of 7 registers.  The specifications state that 56kb
     is the maximum baud rate.

     8250A

     I believe the 8250A is the 8250 with some bug fixes.  I have no idea
     what the bugs may have been.  A quick glance at the specifications
     shows the speed of the 8250 and 8250A to be much the same.  The 8250A
     added an 8th register.  This additional register enables software to
     detect if an 8250 is installed.  The specifications state that 56kb is
     the maximum baud rate.




                                                                         33

     16450

     The 16450 seems to be a speeded up version of the 8250A.  There is no
     direct way (that I know of) for software to detect the difference
     between an 8250A and a 16450.  I believe the 16450 was developed to
     eliminate the need for software to insert delays between successive
     accesses to the device.  The specifications indicate the 16450 is a
     much faster device than its predecessors.  The additional speed is
     only the speed at which the processor can access the device.  The
     maximum baud rate for the 16450 is still stated at 56kb.  However, I
     have been told by some people that they have run the 16450
     successfully at much higher speeds. I do not believe there was ever a
     16450A.

     16C451

     The 16C451 is a CMOS version of the 16450.  CMOS is a term for the
     material and manufacturing process used to make the part.  CMOS
     typically uses less power than other technologies.  If you are not
     designing hardware, you should view the 16C451 as a 16450.

     16550 (Non A)

     It is hard to find a 16550 (Non A).  I was told by National
     Semiconductor that they did everything they could to get all 16550s
     back.  SIO will detect a 16550 and tell you if you have one.  I am
     told that the 16550 was installed in early PS/2 systems.

     The 16550 was the first shot at a FIFOed version of the 8250 family
     from National semiconductor.  However, I was told by National
     Semiconductor that the FIFOs of the 16550 are not reliable and they
     should not be enabled.  SIO will treat a 16550 like a 16450.  In this
     mode, they are reliable.  National Semiconductor would not provide me
     with a specification for the 16550.  However, I suspect its maximum
     baud rate is the same as the 16550A which is 256kb.

     16550A, 16550AF and 16550AFN

     In the manuals that I have, National Semiconductor does not explain
     the differences between the 16550A and the 16550AF.  I suspect the AF
     part may have a few bug fixes.  I believe the N in AFN describes
     packaging, ceramic versus plastic, DIP versus surface mount etc.

     In the opinion of the author, there is no substitute for the 16550A
     (and its successors) in the 8250 type series.  The 16550A is
     compatible with most software written for the entire family of 8250
     type devices.  Programs that are 16550A aware can provide much
     improved performance over previous devices.


     The maximum baud rate for the 16550A is specified at 256kb.  However,
     due to the hardware design of the PC et al, 115kb is the maximum baud
     rate that can be programmed by software.

     The 16550A can be plugged into the same socket that contains an 8250,




     34

     8250A or 16450.  If your SIO expansion board has the SIO chips in
     sockets, you can upgrade to the 16550A by simply removing the old
     chips and replacing them with 16550As.

     The key to the performance increase of the 16550A is its FIFOs.  It
     has 16 byte FIFOs for both transmit and receive data.

     16550s Made by Western Digital

     I have been told, but I have not verified for myself, that 16550s made
     by Western Digital have a problem with their FIFOs when working at
     2400 baud or below.

     16C551

     The 16C551 is a CMOS version of the 16550AF.  See the above
     description of the 16C451 for a discussion of CMOS.  Do not feel you
     need to upgrade from a 16550A or AF to a 16C551.  There is no gain
     from an existing users point of view.

     16C552

     The 16C552 is two 16C551s on a single chip.

     16C554

     The 16C554 is four 16C551s on a single chip.

     82510

     I believe Intel is the only company that manufactures the 82510.  The
     82510 is feature rich with several modes of operation.  Its default
     mode is to operate as a 16450.  The 82510 has a 4 byte FIFO for both
     transmit and receive data.  A 4 byte FIFO is sufficient to provide
     significant performance over a basic 16450.

     The 82510 is small in size.  Therefore, it is found in many lap tops.

     The 82510 is somewhat of a sleeper.  I believe it would be much more
     widely used if Intel had promoted it more.  However, given a choice
     between the 82510 and the 16550A, I would select the 16550A.




                                                                         35


     16650

     The 16650 by Startech seems a good logical step in the evolution of
     the 8250 type UARTs.  One of the many flavors of the 16650 is a
     package that is pin compatible with the 40 pin (DIP) 16550s.  This
     means that the 16650 can be placed into the same socket as any 16550,
     8250, etc.

     The 16650 has enhanced the FIFOs to 32 bytes, added on chip flow
     control ability, and increases the maximum bit rate to 460800.  The on
     chip flow control is a really nice feature.  On chip flow control
     practically eliminates the possibility of missed receive characters. 
     On chip flow control also means that some devices that require
     immediate attention when it sends Xoff, like the Seiko Label Printer,
     will work much better in environments like OS/2 and Windows.

     The 32 byte FIFOs of the 16650 is an improvement over the 16550, but
     is still a disappointment.  I feel that 1k, or larger, FIFOs would
     have been a much better choice.  When I quizzed Startech about this,
     they replied that the 32 byte FIFOs were chosen to keep the cost down. 
     They added that if the 16650 is successful, they plan a 16750 with
     larger FIFOs.

     The 16650 powers up in a 16550 compatible mode, meaning most software
     written for the 16550 should work.  I have discovered a serious
     incompatibility in the current (Oct 1994) versions of the 16650.  All
     previous UARTS in the 8250 family will issue only a single transmit
     interrupt if no additional data is sent to the UART.  The 16650 on the
     other hand, will issue continuous transmit interrupts making it
     necessary to mask the transmit interrupt.  I quizzed Startech about
     this and was told that a new revision of the chip would be available
     within a few months that would correct this incompatibility.

     16750 from Texas Instruments

     The 16750 from TI is an improvement over the 16550, but the omission
     of software flow control (Xon/Xoff) makes it inferior to the 16650, in
     the opinion of the author.  The 16750 has a 64 byte fifo and hardware
     flow control.  It is a good choice for a uart.




     36


     ComBic

     The ComBic is a very impressive UART used on the Hayes ESP card and
     some others.  The ComBic is basically a 16550 UART with on chip flow
     control and 1k FIFOs and a maximum bit rate of 921600.   Like the
     16650, on chip flow control practically eliminates the possibility of
     missed receive characters.  On chip flow control also means that some
     devices that require immediate attention when it sends Xoff, like the
     Seiko Label Printer, will work much better in environments like OS/2
     and Windows.

     The ComBic has two modes of operation, compatibility mode and enhanced
     mode.  In compatibility mode, the UART acts as a 16550.  However, when
     in compatibility mode, the 1k FIFOs and on chip flow control can still
     be used.  In enhanced mode, software gains the ability to look into
     the FIFOs and determine the exact number of bytes loaded.  This
     feature enables software the use block input and output to the ComBic
     which greatly reduces processor overhead.




                                                                         37


                     Appendix C, Multi-Port Serial I/0 Cards

     I have received many requests for information about multi-port serial
     I/O card.  I will describe the boards that I know about (or have heard
     about) here.  I will add to the list as I receive precise information
     from manufactures, users, or I develop it myself.

     Hayes ESP

     The original ESP (ESP V1) is not supported.  The SIO command line must
     contain the ESP's enhanced I/O port address.  For bit rates exceeding
     180000bps the IRQ MUST be specified for the master port. For lower
     data rates NONE may be specified for the IRQ.  SIO does not search for
     the ESP ports as the Hayes drivers do under DOS/Windows.  This
     searching can (will) break things under OS/2.  The SIO command line
     for an ESP at I/O port 180h using IRQ14 would be as follows:

     DEVICE=path\SIO.SYS (COM1,180,IRQ14) (COM2,188,NONE)

     If you would like the above reflected to DOS sessions as a standard
     COM1 and COM2, then use the following command line:

     DEVICE=path\SIO.SYS (COM1,180:3F8,IRQ14:IRQ4) (COM2,188:2F8,NONE:IRQ3)

     Note that the numbers after the colons ":" are the address and IRQ of
     where the port appears to DOS software running under OS/2.  
     Any IRQ specified for an ESP slave port is ignored.  For those that
     like to have a clean looking CONFIG.SYS, SIO will accept NONE as the
     IRQ specification of an ESP slave port.

     If you wish to use the ESP in Compatibility Mode, simply specify the
     base port address that the ESP's compatibility mode is configured for
     (ie 3F8 when configured for COM1).

     Telcor Tport

     The Telcor Tport is supported in both burst mode and 16450 emulation
     mode.  When in burst mode, the Tport's 16k FIFOs are enabled. 
     Additionally in burst mode, no IRQ is used by the Tport.  In burst
     mode, any IRQ specified for the Tport is ignored.  For those that like
     to have a clean looking CONFIG.SYS, SIO will accept NONE as the IRQ
     specification of a Tport.  An example command line defining a Tport
     card to be used in burst mode; and that is configured for COM1
     follows:

     DEVICE=path\SIO.SYS (COM1,Tport@3F8,NONE:IRQ4)

     The Tport's 16450 Emulation mode simply uses a normal SIO command
     line. eg:

     DEVICE=path\SIO.SYS (COM1,3F8,IRQ4:IRQ4)

     In both examples the "IRQ4" following the colon above, means that the
     virtual IRQs are to be sent to a VDM on IRQ4.




     38

     STB 4COM  (ISA bus)

     I am very impressed with the STB 4COM card, they have almost got it. 
     Yes, it's the same company that makes the VGA cards.  The 4COM card
     uses a 16554 which is the equivalent of four 16550A.  Comm ports can
     use IRQs 2/9, 3, 4, 5, 10, 11, 12, and 15.  Any or all ports can share
     IRQs, and they have done this right.  I tested SIO with all four ports
     of the 4COM on IRQ12 and they worked correctly.  The user can select
     any of the following I/O port address for a comm port: 3F8, 2F8, 3E8,
     2E8, 1A8, 1E8, 1F8, 2A8.

     The 4COM card is priced at $110 and I ordered mine from Prerapture
     Solutions which can be reached by telephone at 1-919-286-1502 for
     information and foreign callers.  In the US orders can be placed by
     calling 1-800-735-5266.  Their mailing address is:
          Prerapture Solutions
          1806 Albany St.
          Durham NC 27705-3135

     Gtek BBS550 (ISA bus)

     The Gtek BBS550 is a communications card with the equivalent of 8
     16550s (in reality two 16554s) UARTS.  Where were these cards 5 years
     ago!  Like the STB 4COM, I am very impressed with the BBS550.  It has
     a wide range of selectable I/O port address, some in the 16 bit range
     (above 3FFh) which can be very useful.  I tested the board with all 8
     ports installed using IRQ3 (although I never had more than 3 ports
     active at the same time).  The board performed well using shared IRQs.

     The BBS550 has 8 RJ-45 connectors (10 pin), 6 of which comes directly
     off the back of the card.  The other two RJ-45 connectors are internal
     and special cables with grommets are supplier for these 2 ports.  The
     cables supplied with the BBS550 expands the RJ-45 out to standard DB-
     25 connectors.

     Gtek is located in St. Louis Mississippi.  Their phone number is 800-
     282-4835 or 601-467-8048.




                                                                         39

     Neotech Quad Serial (MCA bus)

     Well, I just got my first PS/2 system (for testing of SIO) and I am
     using the NeoTech Quad Serial card in that system.  What can I say, it
     works beautifully and interrupt sharing has never been a problem on
     MCA systems.  This card (as shipped) came with four individual 16450
     chips installed, but they were in sockets so I installed 16550 UARTS
     before I installed the card.  The card has one large connector on the
     back of the card and the supplied cable expands that to 4 standard DB-
     25 connectors.  Those of you needing a 4 port card for an MCA system
     contact:

          Neotech Inc
          30295 Solon Industrial Pkwy.
          Solon, Ohio 44139

          Voice     (216) 248-4114
          FAX       (216) 248-5701




     40

                        Appendix D, Advanced SIO Options


     The following is provided for the experienced user.  Inexperienced
     users get themselves into a lot of trouble when trying to use these
     options and they cause an inordinate number of support problems.
     Therefore, the following are unsupported options.  If you use them,
     you must work out the problems yourself or ask a friend how they got
     it working.

     Protection

     Placing a dash "-" or a plus "+" in the fourth parameter position, eg
     (COM1,3F8,IRQ4,-),  causes SIO not to provide any protection for that
     port.  The OS may still protect the port somewhat.  When the dash
     parameter is used the port is wide open (like DOS) for any process to
     access it.  If the plus is used, then DOS/Windows sessions are
     inhibited from turning DTR off.

     Locked Baud Rate

     Placing a colon and a baud rate following the communications port, eg
     (COM1:38400,3F8,IRQ4), causes the port to be locked at that baud rate. 
     No program, OS2 or DOS, is allowed to change the baud rate.

     IRQ Reflection to DOS Process

     Normally the IRQ that is reflected to a DOS process is the same as the
     actual hardware IRQ.  Placing a colon and an additional IRQ following
     the normal IRQ, eg (COM1,3F8,IRQ12:IRQ4), causes SIO/VSIO to reflect
     the IRQ to a DOS process on IRQ4 (in this example) even though the
     real hardware IRQ is IRQ12.  If one wishes SIO to automatically locate
     the hardware IRQ, then the following construct can be used:
     (COM1,3F8,:IRQ4).  Notice that the hardware IRQ is simply NOT
     specified.

     I/O Port Mapping to DOS Process

     Some DOS programs, such as CompuServe's CIM, insist that COM1 be at
     I/O port 03F8, COM2 at 02F8, etc.  On OS/2 systems, comm ports can
     have any I/O port address as specified by a command line.  If COM1 is
     not at I/O port 03F8 for some DOS programs, then COM1 can not be used
     by the DOS program.  The SIO command line allows the I/O ports to be
     mapped to a different address for DOS sessions, eg
     (COM1,FF80:03F8,IRQ12:IRQ4).  In this example, the real COM1 is at
     FF80 on IRQ12, but is reflected to DOS processes on I/O ports 03F8 at
     IRQ4.  It is NOT necessary to map both the I/O port address and the
     IRQ.  When the I/O port is mapped to a DOS session, the UART will
     appear at BOTH I/O port addresses (FF80 and 03F8 in the given
     example).




                                                                         41

                                      Index

     16450 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 33
     16550 (Non A) . . . . . . . . . . . . . . . . . . . . . . . . . . . 33
     16550A  . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 33
     16550AF . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 33
     16550AFN  . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 33
     16550s Made by Western Digital  . . . . . . . . . . . . . . . . . . 34
     16650 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 35
     16750 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 35
     16C451  . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 33
     16C551  . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 34
     16C552  . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 34
     16C554  . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 34
     8250  . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 32
     8250A . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 32
     82510 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 34
     Additional Open . . . . . . . . . . . . . . . . . . . . . . . . . .  8
     Addresses and IRQ for COM3 through COM8 on the PS/2 . . . . . . . . 31
     Addresses and IRQs for COM1 and COM2  . . . . . . . . . . . . . . . 31
     Appendix A, Hardware Notes  . . . . . . . . . . . . . . . . . . . . 31
     Appendix B, SIO Chips . . . . . . . . . . . . . . . . . . . . . . . 32
     Appendix C, Multi-Port Serial I/0 Cards . . . . . . . . . . . . . . 37
     Appendix D, Advanced SIO Options  . . . . . . . . . . . . . . . . . 40
     BBS . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .  2
     Close . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .  8
     ComBic  . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 36
     CompuServe  . . . . . . . . . . . . . . . . . . . . . . . . . . . .  2
     DCB . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .  6-8
     Defacto standard for COM3 and COM4  . . . . . . . . . . . . . . . . 31
     Development and Debugging Tools . . . . . . . . . . . . . . . . . .  4
     Device Control Block  . . . . . . . . . . . . . . . . . . . . . . .  8
     Differences between SIO/VSIO and COM/VCOM . . . . . . . . . . . . . 30
     Distribution  . . . . . . . . . . . . . . . . . . . . . . . . . . .  2
     Driver Initialization . . . . . . . . . . . . . . . . . . . . . . .  6
     DTR . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .  8
     DTR Control Mode  . . . . . . . . . . . . . . . . . . . . . . . . .  8
     Email . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .  2
     ESP in Compatibility Mode . . . . . . . . . . . . . . . . . . . . . 37
     Extended Set Bit Rate . . . . . . . . . . . . . . . . . . . . . . . 13
     FAX . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .  2
     FIFO  . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 33, 34
     File System Requests  . . . . . . . . . . . . . . . . . . . . . . .  6
     First Level Open  . . . . . . . . . . . . . . . . . . . . . . . . .  7
     Gtek BBS550 . . . . . . . . . . . . . . . . . . . . . . . . . . . . 38
     Hold Transmit . . . . . . . . . . . . . . . . . . . . . . . . . . . 16
     I/O Port Mapping to DOS Process . . . . . . . . . . . . . . . . . . 40
     Initial Open  . . . . . . . . . . . . . . . . . . . . . . . . . . .  7
     Input Flush . . . . . . . . . . . . . . . . . . . . . . . . . . . .  7
     Input Status  . . . . . . . . . . . . . . . . . . . . . . . . . . .  6
     Intermediate Close  . . . . . . . . . . . . . . . . . . . . . . . .  8
     IRQ . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .  8
     IRQ Reflection to DOS Process . . . . . . . . . . . . . . . . . . . 40
     Last Close  . . . . . . . . . . . . . . . . . . . . . . . . . . . .  8
     Locked Baud Rate  . . . . . . . . . . . . . . . . . . . . . . . . . 40




     42

     National Semiconductor Corporation  . . . . . . . . . . . . . . . . 32
     Neotech Quad Serial . . . . . . . . . . . . . . . . . . . . . . . . 38
     Open  . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .  7
     Ordering  . . . . . . . . . . . . . . . . . . . . . . . . . . . . .  2
     OS2BVEN . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .  2
     Output Flush  . . . . . . . . . . . . . . . . . . . . . . . . . . .  7
     Output Status . . . . . . . . . . . . . . . . . . . . . . . . . . .  7
     PCMCIA  . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 38
     PMLM.EXE  . . . . . . . . . . . . . . . . . . . . . . . . . . . . .  4
     Protection  . . . . . . . . . . . . . . . . . . . . . . . . . . . . 40
     Query Current Bit Rate  . . . . . . . . . . . . . . . . . . . . . . 21
     Query Current Modem Input Signals . . . . . . . . . . . . . . . . . 25
     Query Current Modem Output Control Signals  . . . . . . . . . . . . 25
     Query Extended Bit Rate . . . . . . . . . . . . . . . . . . . . 13, 22
     Query Line Characteristics  . . . . . . . . . . . . . . . . . . . . 21
     Query Number of Characters in Receive Buffer  . . . . . . . . . . . 26
     Query Number of Characters in Transmit Buffer . . . . . . . . . . . 26
     Query SIO Error . . . . . . . . . . . . . . . . . . . . . . . . . . 27
     Query SIO Event Information . . . . . . . . . . . . . . . . . . . . 28
     Query SIO Status  . . . . . . . . . . . . . . . . . . . . . . . . . 23
     Query Transmit Data Status  . . . . . . . . . . . . . . . . . . . . 24
     Read  . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .  6
     Read Device Control Block (DCB) . . . . . . . . . . . . . . . . . . 29
     Read Enhanced Mode Parameters . . . . . . . . . . . . . . . . . . . 29
     RTS . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .  8
     RTS Control Mode  . . . . . . . . . . . . . . . . . . . . . . . . .  8
     Set Bit Rate  . . . . . . . . . . . . . . . . . . . . . . . . . . . 11
     Set Break Off . . . . . . . . . . . . . . . . . . . . . . . . . . . 14
     Set Break on  . . . . . . . . . . . . . . . . . . . . . . . . . . . 17
     Set Line Characteristics  . . . . . . . . . . . . . . . . . . . . . 12
     Set Modem Control Signals . . . . . . . . . . . . . . . . . . . . . 15
     SIO Chips . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 32
     SIO's Utility (SU.EXE)  . . . . . . . . . . . . . . . . . . . . . .  5
     Start Transmit  . . . . . . . . . . . . . . . . . . . . . . . . . . 16
     STB 4COM  . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 37
     Support . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .  2
     Telcor Tport  . . . . . . . . . . . . . . . . . . . . . . . . . . . 37
     Transmit Byte Immediate . . . . . . . . . . . . . . . . . . . . . . 14
     UART  . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 32
     Updates . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .  3
     VIEWPMLM.EXE  . . . . . . . . . . . . . . . . . . . . . . . . . . .  5
     WHAT IS SIO . . . . . . . . . . . . . . . . . . . . . . . . . . . .  1
     Write . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .  7
     Write Device Control Block (DCB)  . . . . . . . . . . . . . . . . . 17
     Write Extended Mode Parameters  . . . . . . . . . . . . . . . . . . 20
