2 Nov
2001
2 Nov
'01
1:17 p.m.
Well, if you have to repair a terminal with those adders, carry generators, etc,
in it, there's little you can do without them, aside, perhaps from building a
daughterboard with a bunch of programmable parts, or at least one significant
one. The latter always produces the risk of not providing the races that were
designed into the original circuit and therefore failing due to proper design
practice.
Dick
----- Original Message -----
From: "Tony Duell" <ard(a)p850ug1.demon.co.uk>
To: <classiccmp(a)classiccmp.org>
Sent: Friday, November 02, 2001 4:49 PM
Subject: Re: CPU design at the gate level
Ben Franchuk skrev:
I am not sure if 74xxx parts are still being made, but I suspect some of
the more common ones are, at least in HC(T), etc families.
Even with FPGAs and other programmable logic, there are still times when
a few TTL chips make sense even in a commercial product. A lot of
products seem to consist of a microcontroller and a little external
logic. For the latter it doesn't make sense to use an FPGA in a lot of cases.
Even if they're not being made, there's no trouble in getting the more
common parts still. Simple gates, flip-flops, bus buffers, counters,
muxes, decoders, etc.
What are hard/impossible to find are things like RAMs, ALUs, carry
generators, and so on. In general they are only useful to people making
CPUs and similar processing circuits, where there's enough logic to make
it worth using an FPGA (no, I don't much care for them either...). Very
few people (except on this list) want to make a CPU from MSI chips, so
those chips are not made any more.
-tony
Never used the stuff. Since they don't make
TTL any more I kind was
forced into using FPGA's. :).
What? My local electronics shop owner tells me that it isn't as high-prof=
ile
nowadays, but it's quite possible to buy 74 series circuits in any good
electronics shop, right?