11 Jun
2019
11 Jun
'19
10:54 a.m.
On Tue, Jun 11, 2019 at 1:50 PM Paul Berger via cctalk
<cctalk at classiccmp.org> wrote:
The process documented above is essentially the
process I started last
night, but in my case I used a GPIO in my HP 9000-332 to cycle through
the inputs and record the output. It is very handy to have general
purpose parallel I/O for purposes like this. In this case the number of
possible states is reduced as two of the inputs are permanently tied
high. I am well on my well to developing logic equations to feed into
palasm to generate a new JEDEC file which I can then burn into a GAL and
test to see if it is correct.
I have just remembered something that I guess you realised some time
back...
The 16L8 allows you to tri-state outputs under logic control (I think there's
one AND term for the output control of each output). I suspect this is used
in ths PAL, certainly for things like DMAR0 and DMARdy which go onto the
backplane connector (and thus could also be driven by another board).
You'll not spot problems with those signals in a 9816 unless you have a DMA
controller board in one of the DIO slots, but...
-tony