ISA/486 Board Question

From: Fred deBros <fdebros_at_verizon.net>
Date: Sat May 4 17:45:01 2002

Most of the time the IRQ selection is done something like that :


IRQ out from ASIC -----------+---o o------- IRQ_a to bus
                             |
                             +---o o------- IRQ_b to bus
                             |
                             +---o o------- IRQ_c to bus
                             |
                             +---o o------- IRQ_d to bus

In other words there's one IRQ output from the ASIC for each port, and a

jumper block to connect that signal to the right pin on the ISA
connector.

So if the jumper block is missing, or doesn't go to the IRQ line you
want, you can just cut the track (in this case between the ASIC and the
IRQ14 pin) and connect the signal to whichever bus line you want. You
need an ISA bus pinout, but that shouldn't be too hard to find.
-----------------------------------------------------------------------

Nothing to it: I can actually see the lines from the isa bus to the irq
bank of plugs.
------------------------------------------------------------------------
-----
Don't you also need to change the I/O address of the IDE port on the
add-on card? This can sometimes be kludged (if there's no better way) by

inverting one of the address lines going into the ASIC (but watch out it

doesn't move the COM port, say, to clash with something else), or by
using
some logic to fiddle the addresses when it detects the right addresses
for the IDE port.
-----------------------
now that's more artistic!
-----------------------
-tony
-------------

fred
Received on Sat May 04 2002 - 17:45:01 BST