PDP-8 on FPGA project & where is Hans Pufal?

bfranchuk at jetnet.ab.ca bfranchuk at jetnet.ab.ca
Thu Dec 18 23:39:49 CST 2008


Vincent Slyngstad wrote:

> I'm hoping to get around that by declaring TP1...TP4 (and *strobe*, etc.)
> to be the clocks, and re-expressing the latches so that they are clocked
> by an "official" clock.  I don't know yet how well that is working out,
> as it's buried in with the other 188 warnings-of-the-moment.

First goal get it working ... That is why I am staying away from doing a PDP -??
with  CPLD's, I don't have all the knowlage up keeping the same features and
bugs as the original hardware.

>    Vince

Sometime late January, I hope to have the logic for a 20 bit cpu using 5 CPLD's,
I find them a little more DIY freindly than FPGA's.  Expect to have ballpark 
PDP-8/e
speeds with but I have run with .8 us static ram memory cycle because I can't use
the trick the PDP-8 uses for address generation, but run address generation
thru the main adder. That is the price you pay for modern features like a Stack 
pointer
or Index  register. The fun part here is just having I/O pins just to display 
the AC, Mar and data
from the last memory cycle, and a Switch register. Good luck with your design
on those features.
Ben





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