pete@wlbr.EATON.COM (Pete Lyall) (08/19/88)
IRQ HACK INSTRUCTIONS
by Pete Lyall
Maybe you've heard of the IRQ hack that you can perform to the
Deluxe RS-232 pack, so that IRQ interrupts are not 'lost', but
didn't know how to do it. Here's the information you need:
Basically, you are connecting the IRQ pin of the 6551 to the IRQ
pin of the 6809..
On the pak:
Locate the little blue jumper wire near the edge connector. One
of the solder pads it is connected to has the label '1' near it.
Desolder both ends of this jumper, and solder one end of a long
wire (1-2 feet - enough to comfortably reach the back of the
coco) to the solder pad near the '1' label. Burn (with the tip of
the soldering iron) or file a small hole in the side of the pak
so that the wire can be passed through it without being pinched.
Attach a miniature phone plug (male) to the end of the wire.
On the Coco3:
Locate the resistor that does the pullup of the IRQ line (CPU pin
3) to the 5vdc. It is R2, and I believe it is the second from the
left in a cluster of resistors to the right-rear of the 6809 chip
(as seen from the keyboard). Solder a wire to the end of that
resistor that is closest to the keyboard (the side that also ties
to CPU pin 3). Carefully route this wire to the back of the
machine, and mount a miniature female phone jack there.
Poof. That's all there is to it. No software changes are required
- the existing ACIAPAK driver will work (better!) as is. If you
run multiple paks (or other interrupt devices that could benefit
from the IRQ hack), just tie them all together at the male plug
that will plug into the coco3.
If you wish to perform this procedure for the coco2, the majority
of the work is the same, except that the resistor that you should
connect to inside the coco is R14. As verification, ensure that
one side of this resistor ties directly to pin 3 of the 6809,
and tack the wire onto this side.
--
Pete Lyall (OS9 Users Group VP)| DELPHI: OS9UGVP | Eaton Corp.(818)-706-5693
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