15 Apr
2002
15 Apr
'02
1:43 p.m.
Yes, and they save on space and not only because of their size. You don't
have to route unused inputs to Vcc or Gnd, and you don't have to accomodate
the device pinout so much, since YOU get to decide what the order of the
outputs and inputs will be, which facilitates layout.
Dick
----- Original Message -----
From: "Ben Franchuk" <bfranchuk(a)jetnet.ab.ca>
To: <classiccmp(a)classiccmp.org>
Sent: Monday, April 15, 2002 9:05 AM
Subject: Re: TTL computing
Richard Erlacher wrote:
> > Again, agreed. PALs are restricted in what they can do, but the
> > restrictions don't matter for many real-world applications. Perhaps you
> > want to make an address decoder. Typically you need perhaps 2 or 3 (at
> > most) product terms of some of the address lines. That fits easily into
a
> > PAL.
> >
> They offer flexibility beyond the capability of any PROM, but they don't
> replace what a PROM was intended to do. A lot of the special-purpose
devices
> have gone by the wayside, e.g. the XOR PALs once
popular for counters and
the
> like, and the 'L' and 'R' types
in favor of the 'V' types. That suggests
that
> the PAL family, truly the simplest of the
programmable logic devices, has
been
refined
considerably. Unfortunately
I think this was because they expected PAL's to replace TTL. CPLD's now
do that job.
But then with higher CPU speeds, PALs have been the work horse of
address decoding and glue logic enables.
--
Ben Franchuk - Dawn * 12/24 bit cpu *
www.jetnet.ab.ca/users/bfranchuk/index.html