























                                     USERS MANUAL

              SIO.SYS and VSIO.SYS, Serial Communications Device Driver
               for OS/2 V2 (and up) and its Virtual DOS Machines (VDM).

                        Copyright (c) 1993 by Raymond L. Gwinn
                                 12469 Cavalier Drive
                              Woodbridge, Virginia 22192
                                 All Rights Reserved

                                    June 15, 1993

                                        Email
                                 CompuServe 72570,157
                          Internet 72570.157@compuserve.com
                         FidoNet 1:265/104 (Routed Mail Only)

                                         FAX
                                     703-494-0595







                                                                          i







                                     INTRODUCTION

          SIO.SYS and VSIO.SYS are  companion device drivers for Version  2
          (and up) of the OS/2 operating system.

          Both drivers (SIO/VSIO) have been coded with performance in mind,
          possibly sacrificing  some compatibility.   For this  reason, SIO
          and VSIO are not exact replacements for the  OS/2 drivers COM and
          VCOM.  However, all serial  communications programs tested by the
          author work correctly using SIO/VSIO.

          This manual is intended for the SIO user.  A separate Application
          Programmers manual is being written.

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

          Product 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.

          Email and  FAX are the  only methods of support  provided.  Voice
          support would overwhelm the author.  If, after reading the manual
          carefully, you are unable  to resolve a problem, please  fill out
          PROBLEM.TXT (adding information as necessary) and Email/FAX it to
          one of the following addresses:

                                        Email
                                 CompuServe 72570,157
                          Internet 72570.157@compuserve.com
                         FidoNet 1:265/104 (Routed Mail Only)

                                         FAX
                                     703-494-0595

          PROBLEM.TXT is included in the distribution ZIP.







                                                                         ii

                                  TABLE OF CONTENTS


          INTRODUCTION  . . . . . . . . . . . . . . . . . . . . . . . .   i
               Product Support  . . . . . . . . . . . . . . . . . . . .   i

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

          WHAT IS VSIO  . . . . . . . . . . . . . . . . . . . . . . . .   2

          GETTING STARTED . . . . . . . . . . . . . . . . . . . . . . .   3

          Installing SIO/VSIO . . . . . . . . . . . . . . . . . . . . .   3
               Quick Start  . . . . . . . . . . . . . . . . . . . . . .   3

          COMMAND LINE OPTIONS  . . . . . . . . . . . . . . . . . . . .   4
               COM1 thru COMn . . . . . . . . . . . . . . . . . . . . .   4
               I/O port address . . . . . . . . . . . . . . . . . . . .   4
               IRQ number . . . . . . . . . . . . . . . . . . . . . . .   4
               Forced 16550A  . . . . . . . . . . . . . . . . . . . . .   4

          AUTOMATIC IRQ ASSIGNMENT  . . . . . . . . . . . . . . . . . .   5

          DOS SETTINGS  . . . . . . . . . . . . . . . . . . . . . . . .   6
               SIO_Allow_Access_COMn  . . . . . . . . . . . . . . . . .   6
               SIO_Virtualize_COM_Ports . . . . . . . . . . . . . . . .   6
               SIO_Virtualize_16550A  . . . . . . . . . . . . . . . . .   6
               SIO_Virtual_RTS_is_HS  . . . . . . . . . . . . . . . . .   6

          Differences between SIO/VSIO and COM/VCOM . . . . . . . . . .   7

          PROBLEMS AND SOLUTIONS  . . . . . . . . . . . . . . . . . . .   8
               IRQ for a port appears to be wrong . . . . . . . . . . .   8
               The modem will not initialize  . . . . . . . . . . . . .   8
               WinFax locks up during install . . . . . . . . . . . . .   8
               WinFax does not work well  . . . . . . . . . . . . . . .   8
               Telemate does not recognize VX00 as a FOSSIL . . . . . .   8
               Output is very slow at 2400 baud and below . . . . . . .   8
               FaxWorks' driver FMD.SYS . . . . . . . . . . . . . . . .   9

          IRQ SHARING ON ISA  . . . . . . . . . . . . . . . . . . . .    10

          Appendix A, Hardware Port and IRQ Assignments . . . . . . .    11
               Addresses and IRQs for COM1 and COM2 . . . . . . . . .    11
               Defacto standard for COM3 and COM4 . . . . . . . . . .    11
               Addresses and IRQ for COM3 through COM8 on the PS/2  .    11

          Appendix B, SIO Chips . . . . . . . . . . . . . . . . . . .    12
               8250 . . . . . . . . . . . . . . . . . . . . . . . . .    12
               8250A  . . . . . . . . . . . . . . . . . . . . . . . .    12
               16450  . . . . . . . . . . . . . . . . . . . . . . . .    13
               16C451 . . . . . . . . . . . . . . . . . . . . . . . .    13







                                                                        iii

               16550 (Non A . . . . . . . . . . . . . . . . . . . . .    13
               16550A . . . . . . . . . . . . . . . . . . . . . . . .    13
               16550AF  . . . . . . . . . . . . . . . . . . . . . . .    13
               16550AFN . . . . . . . . . . . . . . . . . . . . . . .    13
               16550s Made by Western Digital . . . . . . . . . . . .    14
               16C551 . . . . . . . . . . . . . . . . . . . . . . . .    14
               16C552 . . . . . . . . . . . . . . . . . . . . . . . .    14
               16C554 . . . . . . . . . . . . . . . . . . . . . . . .    14
               82510  . . . . . . . . . . . . . . . . . . . . . . . .    14

          Appendix C, Multi-Port Serial I/0 Cards . . . . . . . . . .    15
               STB 4COM . . . . . . . . . . . . . . . . . . . . . . .    15

          INDEX . . . . . . . . . . . . . . . . . . . . . . . . . . .    16







                                                                          1

                                     WHAT IS SIO

          SIO is  a Serial Input/Output  (SIO) communications  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.    SIO.SYS  does not  support  some
          features  that are  provided  by COM.SYS.    In the  view of  the
          author,  these features  are rarely  used and  they inhibit  good
          performance on the vast majority of systems.  See the programmers
          reference manual  for  information about  the  known  differences
          between COM.SYS and SIO.SYS.

          SIO only works with 8250 (TYPE) serial I/O devices.  Such devices
          include  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 to use SIO before
          you will gain benefit.







                                                                          2

                                     WHAT IS VSIO

          VSIO  is a Virtual Device  Driver (VDD).   Virtual device drivers
          provide services  for DOS  programs executing under  OS/2.   Most
          Virtual Device Drivers emulate  a specific hardware device and/or
          BIOS service.   The primary job of a Virtual  Device Driver is to
          convert   misbehaved   DOS   input/output   into   well   behaved
          input/output.

          Using the protection mechanism  of the 386 (and up)  processor, a
          Virtual Device Driver can instruct OS/2  to trap all input/output
          for  given hardware  ports.   Once  trapped,  the Virtual  Device
          Driver   (VDD)  appropriately  routes   information  to/from  the
          Physical Device Driver (PDD) and to/from the DOS program.

          VSIO creates  a  virtual (imaginary)  16550A or  16450 (UART)  in
          software.   VSIO does not emulate any  BIOS services.  All of the
          hardware  registers of  the virtual  UART are simulated  by VSIO.
          VSIO does not attempt  to simulate the timing of the  real UARTs.
          DOS programs that depend on the timing of real hardware UARTs may
          have problems executing under VSIO.

          All  DOS programs  that execute  under VSIO  should  have RTS/CTS
          handshaking  enabled regardless of the baud rate.  Note that this
          enabling  of RTS/CTS  handshaking is  independent of  the RTS/CTS
          handshaking used by SIO.

          The virtualization (simulation) provided by  VSIO is not (and can
          not  be) exact.  However,  most well written  DOS programs should
          not have problems.

          VSIO  will only  work  with SIO  installed  and the  versions  of
          SIO/VSIO must match.  If VSIO refuses to install, you most likely
          have  a version  mismatch.   VSIO will  not work  with  any other
          device driver like COM.SYS.







                                                                          3

                                   GETTING STARTED

          Installing SIO/VSIO

          SIO  is distributed  as a  ZIP file.   To extract  the individual
          files  from the distribution file you need the program PKUNZIP or
          an  equivalent.   PKUNZIP  is  a product  of  PKWARE  and can  be
          downloaded from  almost any  bulletin  board system  (BBS).   You
          probably already have PKUNZIP and know how to use it, otherwise I
          doubt that  you would be reading  this.  When PKUNZIP  is used to
          extract the various files, -AV should appear after each file name
          as it is extracted.  In addition, the message:

               Authentic files Verified!

          should appear after the extraction process.  If this message does
          not appear, or appears with a  name other than Raymond L.  Gwinn,
          the file is not an original SIO distribution file.

          The  only file  that the  basic user  actually needs  is SIO.SYS.
          Virtual  DOS machine (VDM) users  will also want  VSIO.SYS.  Copy
          one  or  both  of  these  files  to  a  convenient  directory  or
          subdirectory on your system.

          Quick Start

          Copy  SIO.SYS and  VSIO.SYS to  the root  directory of  your boot
          drive or diskette.

          If you  are going to  use standard  communications ports,  either
          COM1 or COM2 on an  ISA buss (AT or clone), or  COM1 through COM4
          on a PS/2, then add the following line to your CONFIG.SYS file:

               DEVICE=SIO.SYS
               DEVICE=VSIO.SYS

          Be sure to REMark out the COM.SYS and VCOM.SYS device  drivers if
          they exist in your CONFIG.SYS.

          With the above  statements you will be able to  use standard COM1
          and/or COM2 (if they exist) on any PC system know to the author.

          If your setup is more complex, you must read on.







                                                                          4

                                 COMMAND LINE OPTIONS

          The  command line options are  included in the  command line that
          loads SIO  in the  CONFIG.SYS  file.   VSIO has  no command  line
          options.  Command line options are usually grouped by port within
          parenthesis.

          If you  use only COM1 and/or  COM2, at the standard  IRQ and port
          addresses,  you will not need any command line options.  However,
          up  to four serial communications  ports, COM1 thru  COM4, can be
          specified at any base port address and any IRQ.   On PS/2 systems
          and some  ISA  cards, SIO/VSIO  supports multiple  communications
          devices sharing the same IRQ.

          The basic command line syntax is as follows:

               DEVICE=SIO.SYS (Cn, An, In, Ig, Fc) [(Cn, An, In, Ig, Fc)]

          Where
               "Cn"  is the comm port number (1  thru 4) or the string COM1
               thru COMn.

               "An" is a  hexadecimal number that defines the base hardware
               I/O port address for the communications port.

               "In" is  an IRQ number (0  thru 15) or the  string IRQ0 thru
               IRQ15.  Is  is best if one allows SIO  to determine the IRQ,
               see AUTOMATIC IRQ ASSIGNMENT below.

               "Ig"  is an ignored parameter.   If exists for compatibility
               with COM.SYS.

               "Fc" is the Forced 16550A chip parameter.  If an F is placed
               in  this  position,  a  16550A  UART  chip  type  is  forced
               regardless of the automatically detected chip type.

          For  a PC  with  COM1 and  COM2  of standard  configuration,  the
          following command line will load SIO correctly:

               DEVICE=SIO.SYS (1, 3F8, 4) (2, 2f8, 3)

          A more readable, but identical, command line is:

               DEVICE=SIO.SYS (COM1,3F8,IRQ4) (COM2,2F8,IRQ3)

          Forcing a 16550A on COM1 would be as follows:

               DEVICE=SIO.SYS (COM1,3F8,IRQ4,,F) (COM2,2F8,IRQ3)

          In a similar manner,  up to four serial communications  ports can
          be defined and supported by SIO and VSIO.







                                                                          5


                               AUTOMATIC IRQ ASSIGNMENT

          SIO  will  automatically  locate the  IRQ  that  a  comm port  is
          attached  to.   The  IRQ used  by SIO  for a  given comm  port is
          assigned in the following manner:

          1 - If an IRQ is specified  in the SIO command line then that IRQ
          is used.  However, SIO will  display a warning message if the IRQ
          seems to be other than specified.

          2 -  If no  IRQ is  specified in  the command  line,  and if  SIO
          detected the IRQ then the detected IRQ is used.

          3 - If no  IRQ is specified in the command, and  if SIO could NOT
          detect  an IRQ then  the default IRQ  for the comm  port is used.
          SIO will also display a warning message in this case.

          The following STYLE command  line is recommended for all  but the
          most unusual systems.  That is, specify only the  port number for
          those above COM2 (to tell SIO to support those ports) and let SIO
          do the rest.

          DEVICE=SIO.SYS (COM3) (COM4)

          If you do not have  a COM3 or COM4, or if the mouse  is using the
          only  comm port above COM2 then the following command line should
          be used.

          DEVICE=SIO.SYS







                                                                          6

                                     DOS SETTINGS

          VSIO  gets  its operational  characteristics  from  DOS Settings.
          Several basic DOS Settings  are provided.  They specify  the type
          of  access  (if  any)  that  a  DOS  program  is  to  have  to  a
          communication port that SIO controls.

          All of the  DOS Settings default  to what  most users should  use
          most of  the time (which is  ON).  Also, all of  the DOS Settings
          are prefixed with SIO_.

          The provided DOS Settings and their meaning follow:

               "SIO_Allow_Access_COMn" (where  n is  1 thru  4).  This  DOS
               setting defaults  to ON.  If this  setting is turned OFF for
               any or all of the ports, the DOS program will not be allowed
               any access to that port(s).

               "SIO_Virtualize_COM_Ports"  This Dos setting defaults  to ON
               and it applies to  all communications ports used by  the DOS
               session.  When ON, this DOS  setting means VSIO is to act as
               an interface between the SIO and the DOS program.  When OFF,
               the DOS program is given direct access to the hardware ports
               of the UART(s).

               "SIO_Virtualize_16550A"  This DOS setting defaults to ON and
               it  applies to  all  communications ports  used  by the  DOS
               session.  When ON, VSIO will  simulate a 16550A.  When  OFF,
               VSIO will simulate a 16450.   Some DOS programs may not work
               when  a 16550A is simulated.   Turning this  setting off may
               allow the program to work (but slower).

               "SIO_Virtual_RTS_is_HS"  This DOS setting defaults to ON and
               it applies  to  all communications  ports  used by  the  DOS
               session.  When ON,  VSIO treats RTS as a  handshaking signal
               from the DOS session.  When OFF, VSIO passed the RTS setting
               directly to  the hardware.  This setting  MUST be on for all
               high speed DOS communications.   The only application, known
               to  the author, where this signal may (should) be turned off
               is DOS programs that use true half duplex.







                                                                          7

                      Differences between SIO/VSIO and COM/VCOM

          What  follows is  some  of the  differences between  SIO/VSIO and
          COM/VCOM that are know 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 uses 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  always  controls  the  FIFOs  of  the  16550  UART.
               SIO.SYS will  not allow an application program  (OS2 or DOS)
               to disable the FIFOs of a real 16550.

          5 -  SIO.SYS  will accept any number  between 50 and  115200 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.

          6 -  The last decimal digit of  a baud rate given to SIO  must be
               zero.  SIO.SYS will not support baud rates like 75 or 134.5.
               If given, they will be rounded to 80 and 130 respectively.

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

          8 -  VSIO optionally (and by default)  simulates a 16550A for DOS
               sessions.  VCOM simulates a 8250/16450.







                                                                          8


                                PROBLEMS AND SOLUTIONS

          1 -  Port already in use is displayed.

               This message is displayed when the  comm port or the IRQ  is
               in use.  If the comm port is not actually in use, the IRQ is
               most likely in use.

          2 -  SIO  displays  a warning  message that  the  IRQ for  a port
               appears to be wrong, but the port works.

               SIO probably detected more than one IRQ attached to the comm
               port.  This  indicates a possible hardware problem with your
               system that you may want to have checked.

          3 - The modem will not initialize.

               Configure  your comm  program(s) to  insert a  delay between
               modem  initialization characters  as  they are  sent to  the
               modem.

          4 - WinFax locks up during install.

               During  the  WinFax install,  temporally  turn  OFF the  DOS
               setting  SIO_Virtualize_COM_Ports.    Once  installation  is
               complete,   the   setting  SIO_Virualize_COM_Ports   can  be
               restored.

          5 - WinFax does not work well.

               The  modem init strings set by WinFax (for some modems) will
               work in  the single-layered comm  world of DOS  and Windows.
               However, these  modem  init strings  will  not work  in  the
               multi-layered comm environment used by OS/2.   Specifically,
               in some cases, WinFax sets Xon/Xoff flow control (only) with
               the modem.  Ideally,  both Xon/Xoff and Hardware handshaking
               needs to be set.   If only one handshake can be set, set the
               modem to Hardware handshake.  For USR FAX modems, use &H3.

          6 - Telemate does not recognize VX00 as a FOSSIL.

               Set the baud rate in Telemate to less than 57600.

          7 - Output is very slow at 2400 baud and below.

               This is a  bug in  several BBS programs  that originated  in
               QuickBBS.   The problem has  been corrected  in QuickBBS  by
               Steve Gabrilowitz,  QuickBBS's current author.   Inform  the
               author  of your comm program  of the problem  and to contact
               Steve Gabrilowitz for additional information.







                                                                          9


          8 -  FaxWorks' driver FMD.SYS cannot access a  comm port when SIO
               is used, but works okay with COM.SYS.

               The problem may be that the comm port  is in use (often by a
               DOS program).   In all cases known  to the author,  this has
               been the  case.  That  is, FMD.SYS  can not access  the port
               because  it is  in  use, and  FMD.SYS  does not  report  the
               problem in a manner that is understandable to many users.

               COM.SYS seems  to have a bug  that will allow  an OS2 device
               driver (like FMD.SYS)  to use a comm port when  it is in use
               by  a another device driver, and it (COM.SYS) does not cause
               an  error when it  should.  The exact  conditions of this is
               not fully understood by the author and the above supposition
               may not be totally correct.







                                                                         10

                                  IRQ SHARING ON ISA

          Sharing the  same IRQ for  multiple communications  ports on  ISA
          systems is not  for the weak  of heart  (or mind).   If you  have
          problems  with shared IRQs, DO  NOT contact the  author.  Contact
          the board or computer manufacturer for help.

          Some general rules are as follows:

          1 - Two different  boards (plugged into different slots)  can not
          share the same IRQ.  This is a hardware limitation of ISA systems
          and can  not be corrected by  software.  This means  that you can
          not plug  in two internal modems,  set them for the  same IRQ and
          expect them to work.   This does not apply to PS/2  systems.  The
          problem  of multiple boards sharing the same IRQ was corrected in
          the PS/2's buss design.

          2 - SIO can not (will not) share an IRQ with other device drivers
          at  the same time.   SIO releases  IRQs that it  is currently not
          using.    This  is  different  form  how  COM.SYS  works.    This
          difference may show  up as  an unexpected "port  already in  use"
          error that  does not occur with COM.SYS.  I have received reports
          that the SDLC  drivers try  to concurrently share  IRQs with  the
          ASYNC driver.  SIO.SYS will not allow this while COM.SYS will.







                                                                         11

                    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 (know to the author) prior to the  PS/2 only used 12 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 standard addresses, only the low 12 bits of the address
          are used.   That is,  the high digit  of the  hexadecimal address
          will be ignored.   This means that any  reference to COM3 through
          COM8 will actually address ports 220h through 22Fh.

          You  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.







                                                                         12

                                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 that I know, 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.







                                                                         13

          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.







                                                                         14


          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, 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.







                                                                         15

                       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 users or develop it myself.

          My personal experience  and testing of SIO  is with a board  from
          B&B computer.   However,  I had  to modify the  board to  make it
          share IRQs.  Therefore I will not discuss this board.

          STB 4COM  (ISA buss)

          I am very impressed with the STB 4COM card, they  have almost got
          it.   Yes, its 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.

          I purchased my 4COM  card (for $119) from Steve  Winter, 800-735-
          5266 or 919-286-1502.







                                                                         16

                                        INDEX

          16450 . . . . . . . . . . . . . . . . . . . . . . . . . . . .  13
          16550 Non A . . . . . . . . . . . . . . . . . . . . . . . . .  13
          16550A  . . . . . . . . . . . . . . . . . . . . . . . . . . .  13
          16550AF . . . . . . . . . . . . . . . . . . . . . . . . . . .  13
          16550AFN  . . . . . . . . . . . . . . . . . . . . . . . . . .  13
          16550s Made by Western Digital  . . . . . . . . . . . . . . .  14
          16C451  . . . . . . . . . . . . . . . . . . . . . . . . . . .  13
          16C551  . . . . . . . . . . . . . . . . . . . . . . . . . . .  14
          16C552  . . . . . . . . . . . . . . . . . . . . . . . . . . .  14
          16C554  . . . . . . . . . . . . . . . . . . . . . . . . . . .  14
          8250  . . . . . . . . . . . . . . . . . . . . . . . . . . . .  12
          8250A . . . . . . . . . . . . . . . . . . . . . . . . . . . .  12
          82510 . . . . . . . . . . . . . . . . . . . . . . . . . . . .  14
          Addresses and IRQ for COM3 through COM8 on the PS/2 . . . . .  11
          Addresses and IRQs for COM1 and COM2  . . . . . . . . . . . .  11
          Allow_Access_COMn . . . . . . . . . . . . . . . . . . . . . . . 6
          Appendix A, Hardware Notes  . . . . . . . . . . . . . . . . .  11
          Appendix B, SIO Chips . . . . . . . . . . . . . . . . . . . .  12
          Appendix C, Multi-Port Serial I/0 Cards . . . . . . . . . . .  15
          AUTOMATIC IRQ ASSIGNMENT  . . . . . . . . . . . . . . . . . . . 5
          COMn already in use . . . . . . . . . . . . . . . . . . . . . . 8
          CONFIG.SYS  . . . . . . . . . . . . . . . . . . . . . . . . . . 3
          Defacto standard for COM3 and COM4  . . . . . . . . . . . . .  11
          Differences between SIO/VSIO and COM/VCOM . . . . . . . . . . . 7
          DOS SETTINGS  . . . . . . . . . . . . . . . . . . . . . . . . . 6
          FaxWorks  . . . . . . . . . . . . . . . . . . . . . . . . . . . 9
          FIFO  . . . . . . . . . . . . . . . . . . . . . . . . . .  13, 14
          FMD.SYS . . . . . . . . . . . . . . . . . . . . . . . . . . . . 9
          GETTING STARTED . . . . . . . . . . . . . . . . . . . . . . . . 3
          Installing SIO/VSIO . . . . . . . . . . . . . . . . . . . . . . 3
          IRQ . . . . . . . . . . . . . . . . . . . . . . . . . . . .  4, 5
          IRQ SHARING ON ISA  . . . . . . . . . . . . . . . . . . . . .  10
          National Semiconductor Corporation  . . . . . . . . . . . . .  12
          PDD . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2
          Physical Device Driver  . . . . . . . . . . . . . . . . . . . . 2
          PKUNZIP . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3
               Authentic files  . . . . . . . . . . . . . . . . . . . . . 3
          PROBLEMS AND SOLUTIONS  . . . . . . . . . . . . . . . . . . . . 8
          Quick Start . . . . . . . . . . . . . . . . . . . . . . . . . . 3
          RTS/CTS handshaking . . . . . . . . . . . . . . . . . . . . . . 2
          SIO Chips . . . . . . . . . . . . . . . . . . . . . . . . . .  12
          SIO_Virtual_RTS_is_HS . . . . . . . . . . . . . . . . . . . . . 6
          STB 4COM  . . . . . . . . . . . . . . . . . . . . . . . . . .  15
          UART  . . . . . . . . . . . . . . . . . . . . . . . . . . . .  12
          VDD . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2
          Virtual Device Driver . . . . . . . . . . . . . . . . . . . . . 2
          Virtualize_16550A_For_COM . . . . . . . . . . . . . . . . . . . 6
          Virtualize_COM_Ports  . . . . . . . . . . . . . . . . . . . . . 6
          WHAT IS SIO . . . . . . . . . . . . . . . . . . . . . . . . . . 1
          WHAT IS VSIO  . . . . . . . . . . . . . . . . . . . . . . . . . 2







                                                                         17

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