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IRQ.FAX
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1994-12-10
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Assignment of IRQ Levels (CP 3/15/94
OS2IRQ.FAX ASSIGNMENT OF IRQ LEVELS
Interrupt Request (IRQ) Levels
On an ISA machine there are a total of 15 IRQ levels available.
Many of these are already being used. Most are already in use
because they are the standard settings for the common devices.
These standard setings are as follows:
IRQ LEVEL DEVICE ASSOCIATED
0 System Timer
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 idential with
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 will actually be 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 ports, you
are likely to find these levels available to use without conflict
with some other adapter. Furthermore, if you don't have two
parallel ports installed, IRQ5 might be usable for some other
purpose, such as COM3 or COM4. Be cautious about doing this
because it might cause a problems later if you decide to install
a second parallel port. In addition, some other nonstandard
device might be using IRQ5.
Enabling COM Ports
The original ISA computer (the IBM Personal Computer AT*) allows
for the definition of up to four 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.
Over the years, a convention has developed that places the port
addresses for COM3 and COM4 at 03E8 and 02E8 respectively. This
is 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 you have checked and set I/O and IRQ values on your COM
ports or internal modems, you must add this information to the
communications device-driver (COM.SYS) statement in CONFIG.SYS.
You might also need to tell your communications program where
COM ports are. If the program, operating system, and hardware
are not in agreement, then 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, you can define COM ports that do not
have any physical adapters attached in the COM.SYS statement.
These substitute definitions will serve as placeholders. 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 accomodate your particular configuration.
The following parameter needs to 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 non-standard IRQ.
To enable COM3 or COM4, place following in CONFIG.SYS file:
DEVICE=X:\OS2\COM.SYS (n,x,i,s)
where: X = The drive where OS/2 is installed
n = The communication port number (1,2,3,4)
a = The communication port I/O address in hex (for
example, 03E8 02E8, 2320).
i = IRQ level. Valid settings are 1 to 15 (decimal)
s = The spurious interrupt handling switch. Valid
settings are D or I. The D setting uninstalls
COM driver if more than 1000 spurious interrupts
come in consecutively. The I setting ignores
spurious interrupt. This setting is optional.
For example, to install COM3 at address 03E8 on IRQ5 (assuming
that OS/2 is installed on drive C):
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 can be set to a range of values via jumpers or
switches. In some cases you might find the values are fixed
or 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 that you cannot use
both adapters at the same time.
You may read this and more detailed information on Pgs. 375 -
383 in the OS/2 2.1 Using the Operating System Guide.
-----------------------------------------------------------------
DISCLAIMER: The information contained in this document is
distributed "AS IS" without any warranties of any kind either
express or implied. IBM will not be responsible for any direct,
incidental, consequential, special or indirect damages. IBM
EXPRESSLY DISCLAIMS ANY IMPLIED WARRANTY OF MERCHANTABILITY AND
ANY IMPLIED WARRANTY OF FITNESS FOR A PARTICULAR PURPOSE.
The use of this information or the implementation of any of these
techniques is the sole responsibility of the customer and depends
on the customer's ability to evaluate and integrate this
information or implementation into the customer's operational
environment.
------------------------------------------------------------------
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