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1996-11-12
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OSCPIRQ - ASSIGNING IRQ LEVELS AND ENABLING COM PORTS -
ALL OS/2 RELEASES
01/23/96
=======================================================================
Assigning IRQ Levels and Enabling COM Ports--All OS/2 Releases
=======================================================================
Please Read Entire Document for Full Explanation of Procedures
--------------------------------------------------------------
DESCRIPTION
This document helps you determine the IRQ settings you can use for COM3
or COM4 port adapters to avoid shared interrupts.
RESOLUTION
On an ISA computer, 15 IRQ levels are available. Most are already in
use because they are the standard settings for common devices. These
standard settings are:
IRQ Level Device
--------- ------
0 System
1 Keyboard
2 Secondary Interrupt Controller (see Note)
3 COM2 (Serial Communications Port 2)
4 COM1 (Serial Communications Port 1)
5 LPT2 (Parallel Port 2)
6 Diskette
7 LPT1 (Parallel Port 1)
8 Real-time Clock
9 Open
10 Open
11 Open
12 Auxiliary Port (Mouse)
13 Math Coprocessor
14 Hard Disk
15 Open
Note: On the IBM AT (ISA bus), the IRQ9 pin is identical to the IRQ2
pin on the original IBM PC. If you have an earlier, 8-bit adapter
whose documentation states that it uses IRQ2, be aware that this
is actually interpreted as IRQ9 when plugged into the 16-bit ISA
bus.
The IRQ levels shown as Open have no established, standardized
use. When setting IRQ values on your COM3 or COM4 port, you might
find these levels available to use without conflict with some
other adapter. If you do not have two parallel ports installed,
IRQ5 might be usable for another purpose, such as COM3 or COM4.
Be cautious about doing this; it might cause a problem later if
you decide to install a second parallel port. Also, another
nonstandard device might be using IRQ5.
Enabling COM Ports
------------------
The original ISA computer (the IBM Personal Computer AT) allowed for
the definition of up to 4 serial communications ports. However, there
has never been any hardware architectural standard that defined the I/O
port addresses or IRQ lines associated with communication ports 3 and 4.
A convention places the port addresses for COM3 and COM4 at 03E8 and
02E8, respectively. This is a generally accepted convention, but not a
standard. Check the documentation and the settings of the adapters in
your system to verify your hardware environment.
After checking and setting the I/O and IRQ values on your COM ports or
internal modems, you must add this information to the communications
device-driver statement (COM.SYS) in the CONFIG.SYS file.
You might also need to tell your communications program where the COM
ports are. If the program, operating system, and hardware are not in
agreement, the program will not run.
OS/2 COM ports do not need to be defined in sequence. It is acceptable
to have a COM4 without having a COM3. However, DOS might have
difficulty if there is a gap in the port definition. To avoid confusion
for DOS, define COM ports that do not have any physical adapters
attached in the COM.SYS statement. These substitute definitions will
serve as place holders. COM1 and COM2 are assumed to have standard
values and do not need to be explicitly set up unless you want to set
some nonstandard values to accommodate your particular configuration.
The following parameter must be specified for COM3 and/or COM4 on
ISA/EISA bus systems. Micro Channel bus systems do not need to specify
this parameter unless the system has a COM port with a nonstandard COM
port address or nonstandard IRQ setting.
To enable COM3 or COM4, place following in the CONFIG.SYS file:
DEVICE=x:*\OS2\COM.SYS (n,x,i,s)
where:
x is the drive where OS/2 is installed
n is the communication port number (1, 2, 3, or 4)
a is the communication port I/O address in hexadecimal; for example,
03E8 02E8, 2320).
i is the IRQ level. Valid settings are 1 to 15 (decimal).
s is the spurious interrupt handling switch. Valid settings are D or
I. The D setting uninstalls COM driver if more than 1000 spurious
interrupts occur consecutively. The I setting ignores spurious
interrupts. This setting is optional.
Example: To install COM3 at address 03E8 on IRQ5 (assuming that OS/2 is
installed on drive C), use the following CONFIG.SYS statement:
DEVICE=C:*\OS2\COM.SYS (3,03E8,5)
The I/O address and IRQ level should be noted in the documentation that
came with your adapter. Either or both might be fixed values, or you
might be able to set a range of values using jumpers or switches. In
some cases, you might find that the range of settings available to you
is insufficient to avoid the sharing conflict. In that case, you must
purchase a different, more versatile adapter, or accept the fact that
you cannot use both adapters at the same time.
______________________________________________________________________
IBM disclaims all warranties, whether express or implied, including
without limitation, warranties of fitness and merchantability with
respect to the information in this document. By furnishing this
document, IBM grants no licenses to any related patents or copyrights.
Copyright (c) 1994, 1995 IBM Corporation. Any trademarks and product
or brand names referenced in this document are the property of their
respective owners. Consult your product manuals for complete trademark
information.