[TUHS] Off-topic: any logic designers here?

Clem Cole clemc at ccc.com
Fri Aug 11 00:35:29 AEST 2017

i agree with Peter, WRT the '181 you can certainly find them in small
qualities in the after market, I may have a handful of them myself.   One
thing you are missing is a small barrel shifter, which the '181 does not
support, but for a 8 bit shift it should not be terrible.   Vaxen and such
built their independently, but it is worth while IMO, as it allows in a
single clock tick to perform pretty substantial arithmetic, although
because it's a sq law the cost in die area is huge. If you look at the 68K
for instance, the big area in the middle everyone sees in the pictures is
the shifter (same for the Alpha chips).


On Thu, Aug 10, 2017 at 4:16 AM, Peter Jeremy <peter at rulingia.com> wrote:

> On 2017-Aug-08 12:52:36 +1000, Warren Toomey <wkt at tuhs.org> wrote:
> >Hi all, sorry for this off-topic posting.
> Well, just promise to port Unix to it and it won't be off-topic.
> >Anyway, I thought it would be fun to do something similar but with
> >a bigger address space and as few chips as I could get away with.
> Well, using a FPGA or microcontroller will reduce the chip count further.
> You suggest that you won't use a 74LS181 because they are no longer made.
> Whilst that's true, they are still readily available as NOS.  Overall, I
> would suggest that using a 74LS181 (or 4) is a cleaner solution than
> (ab)using a couple of EPROMs.  (The other option would be a PAL or GAL but
> I suspect finding and programming them would be more difficult).
> --
> Peter Jeremy
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