OSMKCM03 - CONFIGURING OS/2 FOR ASYNCHRONOUS COMMUNICATIONS
07/09/96

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           Configuring OS/2 for Asynchronous Communications
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Please Read Entire Document for Full Explanation of Procedures
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DESCRIPTION

* Modem doesn't work.

* Modem locks up the system or session when you try to use it.

* Modem works in native DOS and Windows, but doesn't work in
  OS/2, WIN-OS/2, or DOS-OS/2.

* After OS/2 for Windows is installed, the modem doesn't work in
  OS/2.

RESOLUTION

Configure Device Driver for COM3 and COM4
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OS/2 is an interrupt-driven operating system. In an ISA system, OS/2 
requires unique I/O addresses and interrupt-request (IRQ) lines for 
each adapter. If two adapters are sharing the same physical IRQ, the 
processor does not know which adapter and, therefore, which OS/2 
session, should get the IRQ. In a single-tasking operating system, such 
as DOS, the sharing of interrupts is not a problem, because only one 
application at a time is used. With OS/2, if you have three or four 
serial-communications adapters, you might try to use two or more of 
them at the same time. If some of them are set up to share interrupts, 
you will have problems.

To avoid these problems, make sure that all hardware adapters have a 
unique I/O address and unique IRQ assignments. Check and set the 
adapter according to the documentation. Include IRQ Base I/O DMA for 
each slot.

Configure Device Driver for Non-Default COM1 and COM2
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The OS/2 COM.SYS driver recognizes COM1 at I/O address 03F8, IRQ4; it 
recognizes COM2 at I/O address 02F8, IRQ3 (these are known as the 
default standards). It does not know about any other configurations and 
requires the parameters specified below to function with configurations 
that vary from the default standard.

Edit the CONFIG.SYS file for valid COM.SYS parameters, which are:

   DEVICE=x:\OS2\COM.SYS (n, a, i, s, f)

where:

   x = the drive where OS/2 is installed.
   n = the communications port number (1, 2, 3, or 4).
   a = the port I/O address in hex (03F8, 02F8, 2320).
   i = the IRQ level (3, 4, 5,....15 decimal).
   s = the spurious interrupt handler (optional).
   f = 'F' to indicate a 100% buffered NS16550a-compatible UART.
   D = Disable driver if spurious interrupts are greater than
        1000.
   I = ignore (default setting; need not include)

Examples 
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DEVICE=X:\OS2\COM.SYS (1, 3F8, 5, d, f)

   Used when COM1, I/O address 03F8, uses a non-default IRQ of 5;
   the driver is disabled if more than 1000 spurious interrupts
   are received and an NS16550 (buffered) UART is in use.

DEVICE=X:\OS2\COM.SYS (3, 3E8, 10, D)

   Used when COM3, I/O address 03E8, uses an IRQ level of 10, and
   the driver unloads if spurious interrupts are greater than
   1000.

Configure DOS Settings
----------------------
Make sure the DOS settings have:

   COM_DIRECT_ACCESS = OFF
   COM_SELECT = ALL or COMx (x is the port the application is using.)

Configure Application
---------------------
Make sure the application is configured for the correct port and line 
settings. For example, COM3, 8 bits, 1 stop, no parity, 9600 baud.

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