Jan 012018
Text file explaining how to set up OS/2 for compatibility with PPI modems.
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Text file explaining how to set up OS/2 for compatibility with PPI modems.
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Contents of the PPI_OS2.TXT file


Using the Practical Modem 14400FXSA V.32bis with IBM OS/2 2.0

Contrary to what is in the README file of OS/2, this modem can function
perfectly well with OS/2. This document is intended as a guide to help
users configuring their systems to use the PM14400FXSA with OS/2. By
following the tips listed here, you should be able to most DOS, Windows
and OS/2 communications software working with the modem as an OS/2 task.

The user is assumed to have a working knowledge of OS/2 and the
PM14400FXSA modem.

This document is split into the following sections:

1. MODE parameters
2. CONFIG.SYS commands
3. Using Quick Link II Fax
4. DOS settings
5. 8250 UARTs


1. MODE parameters

The following MODE parameters can be used as guidelines in helping the
user determine optimal settings for use with the PM14400FXSA. Note that
only serial ports with a hardware FIFO buffer or DMA capability support
the ENHANCED parameter, and only serial ports with DMA capability support

For DOS programs that can support hardware (RTS/CTS) handshaking:

Some systems do not reliably support 57600 baud DTE speeds. In these
cases, try a slower speed such as 38400 or 19200. The minimum DTE
speed to allow v.32bis (14400 bps) connections is 19200 baud.

These settings are needed to allow automatic protocol-override mode.
The PM14400FXSA should be set for &S0, which is the factory default.

NOTE: Sometimes, using these settings, the application may "freeze."
If this happens, use IDSR=OFF,ODSR=OFF instead. If the application
drops characters with IDSR=OFF,ODSR=OFF, try using BUFFER=ON instead
of BUFFER=AUTO as outlined below. In general, BUFFER=AUTO gives
best results at high serial port speeds.

These settings tell OS/2 not to monitor the CTS line or to control
the RTS line. Instead, OS/2 will allow the DOS application to
monitor CTS and control RTS. The PM14400FXSA should be set for &K3,
which is the factory default. If the application loses data while
other tasks are running, you can let OS/2 take control of the RTS
line with RTS=HS.

This setting tells OS/2 not to control the DTR line. Most programs
use the DTR line to hang up the line and force the modem into command
mode. Normally the PM14400FXSA should be set for &D2.

This setting tells OS/2 to run in automatic protocol-override mode.
This provides maximum serial port performance, and is the optimal
setting for using the PM14400FXSA at high baud rates.

This setting tells OS/2 to run in enhanced mode, which will enable
the FIFO mode or DMA mode of serial ports that allow such operations.

This setting tells OS/2 to use DMA to receive or transmit data over
serial ports that support DMA mode operations. If no DMA channel is
available, FIFO mode is used instead but the data transfer will still

DOS programs that do not know how to use hardware handshaking should use
similar settings, except OS/2 itself should be allowed to perform the
hardware handshaking. This is done by setting OCTS=ON,RTS=HS.

Some DOS programs (such as those under WIN-OS/2) work better with

OS/2 programs can usually manipulate these settings without having the
user set them. However, most OS/2 programs will function best with
OCTS=ON,DTR=ON,RTS=HS and the other above settings.


2. CONFIG.SYS commands

MODE settings for the system can be set automatically in CONFIG.SYS. To
do this, place the following line in between the


(Your drive may not necessarily be C:.)

Additionally, communications tasks may gain better performance by setting
MAXWAIT=1 in CONFIG.SYS. IOPL=YES may also be required for certain
combinations of MODE parameters.

In some extreme cases, PRIORITY_DISK_IO=NO may be required to avoid
losing data with DOS communications software.

On certain systems, OS/2 will not recognize all serial ports on the
system. (This often happens with ISA systems with COM3 and COM4.) To
have OS/2 support serial ports, the DEVICE=C:\OS2\COM.SYS line needs to
be modified. The parameters are as follows:


where n is the COM port, a is the I/O address, and i is the IRQ level.

Multiple ports may be defined this way, such as:

DEVICE=C:\OS2\COM.SYS (3,03E8,5) (4,02E8,10)

would define COM3 at address 3E8 on IRQ5 and COM4 on 2E8 on IRQ10.

ISA systems can have problems in sharing IRQ lines. In general, it's
best to avoid using two devices at the same time with the same IRQ level
on ISA systems.

Micro Channel and EISA systems use level sensitive interrupts and can
normally share IRQ lines reliably.


3. Using Quick Link II Fax

This is the program that ships with the PM14400FXSA.

Quick Link II Fax should work reliably under OS/2 with the above settings
for DOS programs that support hardware handshaking. QL2FAX should itself
be set for 57600 baud and RTS/CTS flow control.

Quick Link II Fax may produce SYS3175 or SYS3176 errors when running in
a DOS session. If this occurs, running QL2FAX in a stand-alone version
of DOS under OS/2. For information about running other versions of DOS
under OS/2, look in Appendix E of the OS/2 Installation Guide (page 97).
(Note that you cannot normally run the OS/2 MODE command in a stand-
alone version of DOS running under OS/2. Set up the serial port before
starting the stand-alone version of DOS.)

NiteFax may cause strange behavior if loaded and the system is left at a
command prompt. The following batch file (NITEFAX2.BAT) should allow
proper NiteFax operation as a DOS task:

ECHO All incoming faxes are received and automatically printed.
ECHO To turn off NiteFax, press any key.

You can now load NiteFax from an icon using NITEFAX2.BAT. By pressing
any key, the DOS session is closed and NiteFax is terminated.

Users that run QL2FAX from a stand-alone version of DOS may want to make
the following text file (EXIT_VDM.DBG). When run through DEBUG, it
creates a file called EXIT_VDM.COM that will end any VDM (Virtual DOS
Machine), including stand-alone versions of DOS. This is useful since
the EXIT command will not end DOS sessions running stand-alone versions
of DOS.

; Enter the following: DEBUG ; This will create the file EXIT_VDM.COM.
; This program will terminate a VDM. It will
; work in both OS/2 DOS Emulation and VM-Boot.
mov ah,4D
int 21
db 2,FD

n exit_vdm.com


4. DOS settings

DOS programs that perform communications may experience a performance
increase by setting HW_TIMER to ON. Some programs can also benefit from
setting IDLE_SECONDS to 60 and IDLE_SENSITIVITY to 100.

Setting HW_ROM_TO_RAM to ON may increase performace on some systems, as
can settinging COM_HOLD to ON.

Remember that in multitasking operating systems such as OS/2, giving more
CPU time to one task (by boosting the IDLE settings) may decrease
performance in other tasks.

Running a program as a full screen application can improve performance as


5. 8250 UARTs

OS/2 may have poor performance for high-speed serial port communications
on systems that use an 8250 UART. Performance can be greatly improved by
using a 16450 or 16550 UART. The 16550AFN can provide a hardware FIFO
buffer as well.


Note: This document was researched and created by an IBM employee who works
with OS/2 on a daily basis. It was created on his own time, using his
own computer and does not represent anything 'official' from IBM. He
is kindly sharing his knowledge and insight with others on how to get
the PM14400FXSA modem and Quick Link II FAX to operate properly under
OS/2 version 2.0.

When there is additional information developed on this topic it will
be posted as an additional file or as a revision to this file.


Paul E. Hansen 76702,475

 January 1, 2018  Add comments

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