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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
┌──────────────────────────────────────┐
│ Item Type │
├───────────────────────────┬──────────┤
│ 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
┌──────────────────────────────────────┐
│ Item Type │
├───────────────────────────┬──────────┤
│ Data Bits Per Character │ BYTE │
├───────────────────────────┼──────────┤
│ Parity Setting │ BYTE │
├───────────────────────────┼──────────┤
│ 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
┌──────────────────────────────────────┐
│ Item Type │
├───────────────────────────┬──────────┤
│ Bit/Baud Rate │ DWORD │
├───────────────────────────┼──────────┤
│ 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
┌──────────────────────────────────────┐
│ Item Type │
├───────────────────────────┬──────────┤
│ 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
┌──────────────────────────────────────┐
│ Item Type │
├───────────────────────────┬──────────┤
│ 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
┌──────────────────────────────────────┐
│ Item Type │
├───────────────────────────┬──────────┤
│ DTR and RTS on mask │ BYTE │
├───────────────────────────┼──────────┤
│ 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
┌──────────────────────────────────────┐
│ Item Type │
├───────────────────────────┬──────────┤
│ 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
┌──────────────────────────────────────┐
│ Item Type │
├───────────────────────────┬──────────┤
│ 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
┌──────────────────────────────────────┐
│ Item Type │
├───────────────────────────┬──────────┤
│ Write Timeout │ WORD │
├───────────────────────────┼──────────┤
│ Read Timeout │ WORD │
├───────────────────────────┼──────────┤
│ Flags1 │ BYTE │
├───────────────────────────┼──────────┤
│ Flags2 │ BYTE │
├───────────────────────────┼──────────┤
│ Flags3 │ BYTE │
├───────────────────────────┼──────────┤
│ Error Replacement Byte │ BYTE │
├───────────────────────────┼──────────┤
│ Break Replacement Byte │ BYTE │
├───────────────────────────┼──────────┤
│ Xon Character │ BYTE │
├───────────────────────────┼──────────┤
│ 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
┌──────────────────────────────────────┐
│ Item Type │
├───────────────────────────┬──────────┤
│ Enhanced Flags1 │ BYTE │
├───────────────────────────┼──────────┤
│ 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
┌──────────────────────────────────────┐
│ Item Type │
├───────────────────────────┬──────────┤
│ Bit/Baud Rate │ WORD │
└───────────────────────────┴──────────┘
See function 41h for more information.
62h - Query Line Characteristics
Parameter Packet - None.
Data Packet
┌──────────────────────────────────────┐
│ Item Type │
├───────────────────────────┬──────────┤
│ Data Bits Per Character │ BYTE │
├───────────────────────────┼──────────┤
│ Parity Setting │ BYTE │
├───────────────────────────┼──────────┤
│ Stop Bit Setting │ BYTE │
├───────────────────────────┼──────────┤
│ 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
┌──────────────────────────────────────┐
│ Item Type │
├───────────────────────────┬──────────┤
│ Current Bit/Baud Rate │ DWORD │
├───────────────────────────┼──────────┤
│ Fraction of Current │ BYTE │
├───────────────────────────┼──────────┤
│ Minimum Bit/Baud Rate │ DWORD │
├───────────────────────────┼──────────┤
│ Fraction of Minimum │ BYTE │
├───────────────────────────┼──────────┤
│ Maximum Bit/Baud Rate │ DWORD │
├───────────────────────────┼──────────┤
│ 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
┌──────────────────────────────────────┐
│ Item Type │
├───────────────────────────┬──────────┤
│ 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
┌──────────────────────────────────────┐
│ Item Type │
├───────────────────────────┬──────────┤
│ 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
┌──────────────────────────────────────┐
│ Item Type │
├───────────────────────────┬──────────┤
│ 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
┌──────────────────────────────────────┐
│ Item Type │
├───────────────────────────┬──────────┤
│ 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
┌──────────────────────────────────────┐
│ Item Type │
├───────────────────────────┬──────────┤
│ Number of Bytes Buffered │ WORD │
├───────────────────────────┼──────────┤
│ Byte Size of the Buffer │ WORD │
└───────────────────────────┴──────────┘
Self explaining.
69h - Query Number of Characters in Transmit Buffer
Parameter Packet - None.
Data Packet
┌──────────────────────────────────────┐
│ Item Type │
├───────────────────────────┬──────────┤
│ Number of Bytes Buffered │ WORD │
├───────────────────────────┼──────────┤
│ Byte Size of the Buffer │ WORD │
└───────────────────────────┴──────────┘
Self explaining.
27
6Dh - Query SIO Error
Parameter Packet - None.
Data Packet
┌──────────────────────────────────────┐
│ Item Type │
├───────────────────────────┬──────────┤
│ 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
┌──────────────────────────────────────┐
│ Item Type │
├───────────────────────────┬──────────┤
│ 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
┌──────────────────────────────────────┐
│ Item Type │
├───────────────────────────┬──────────┤
│ Write Timeout │ WORD │
├───────────────────────────┼──────────┤
│ Read Timeout │ WORD │
├───────────────────────────┼──────────┤
│ Flags1 │ BYTE │
├───────────────────────────┼──────────┤
│ Flags2 │ BYTE │
├───────────────────────────┼──────────┤
│ Flags3 │ BYTE │
├───────────────────────────┼──────────┤
│ Error Replacement Byte │ BYTE │
├───────────────────────────┼──────────┤
│ Break Replacement Byte │ BYTE │
├───────────────────────────┼──────────┤
│ Xon Character │ BYTE │
├───────────────────────────┼──────────┤
│ Xoff Character │ BYTE │
└───────────────────────────┴──────────┘
See function 53h for a description of the parameters.
74h - Read Enhanced Mode Parameters
Parameter Packet - None.
Data Packet
┌──────────────────────────────────────┐
│ Item Type │
├───────────────────────────┬──────────┤
│ Enhanced Flags1 │ BYTE │
├───────────────────────────┼──────────┤
│ 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
