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OS2IRQCP - ASSIGNMENT OF IRQ LEVELS AND ENABLING COMPORTS
12/28/94
================================================================
ASSIGNMENT OF IRQ LEVELS AND ENABLING COMPORTS
================================================================
Please Read Entire Document for Full Explanation of Procedures
----------------------------------------------------------------
INTERRUPT REQUEST (IRQ) LEVELS
The following information helps you determine the IRQ settings
you can use for COM3 or COM4 port adapters to avoid shared
interrupts.
On an ISA machine there are a total of 15 IRQ levels available.
Most are already in use because they are the standard settings
for the common devices. These standard settings are:
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 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 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 may find these levels available for 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
non-standard 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.
A convention 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 checking and setting the I/O and IRQ values on your COM
ports or internal modems, you need to add this information
to the communications device-driver (COM.SYS) statement in the
CONFIG.SYS file.
You may also need to tell your communications program where the
COM ports are. If the program, operating system, and hardware
are not in agreement, then the program does 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 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 non-standard
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 non-standard 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 using 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.
----------------------------------------------------------------
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.