30 Sep
2014
30 Sep
'14
6:01 p.m.
David Cooper wrote:
I have read the pure logic PALs (without registers) by connecting the
address lines from an eprom programmer to the inputs and the data lines to
the outputs. Then read it like an EPROM. From that you can reduce the
logic but that gives you all outputs for all possible input combinations.
That doesn't work if there is a latch programmed into the PAL. The
original PC AT, for example, had two PALs (both 16L8, I think, but it
has been a loooong time). The address decoding one could be read just
fine by the method you indicated but the FPU interface one implemented a
latch on one of its outputs. That stumped cloners in Brazil for nearly
three years (in general - my friends at Softec got it in half an hour.
They were good. And I helped a little)..
-- Jecel