Tony,
Faster as in is sub 150ns are fairly common and cheap. Whats
problemtic is that the ALU must do about 8-16 different operations
so that would be at least a 512kN part or larger.
Also 74(ALS,F,AS)381 in the 16 bit or wider range would be hard
pressed to do better than 50ns even with carry lookahead.
Allison
-----Original Message-----
From: Tony Duell <ard_at_p850ug1.demon.co.uk>
To: classiccmp_at_classiccmp.org <classiccmp_at_classiccmp.org>
Date: Monday, November 05, 2001 7:06 PM
Subject: Re: CPU design at the gate level
>> How about programming an EPROM with a lookup
>> table to emulate an ALU?
>
>Sure, if you want one that takes 250ns or so to produce a result (the
>access time of most cheap EPROMS). The 74x181 is going to be rahter
>faster than that, I think.
>
>I have thought about using fast-ish RAMs (cache rams from old PC
>motherboards) as poor-man's programmable logic. It would run at a
>sensible speed, and wouldn't need proprietry programming tools.
>
>-tony
>
Received on Mon Nov 05 2001 - 20:09:51 GMT