Bipolar PALs and PROMs had one weakness in that they were risky when being
tested, since testing sometimes damaged the fuse array. It took a while for the
programmer makers to develop a way of testing them that didn't damage them as
much as 2% of the time.
I haven't run into any documentation claiming that PALs didn't exist prior to
1978, though most of MMI's data sheets were marked PRELIMINARY in 1978. The
16L/R/X-series was new then, but the 10- 12-and 14 series was earlier than that.
Dick
----- Original Message -----
From: "ajp166" <ajp166_at_bellatlantic.net>
To: <classiccmp_at_classiccmp.org>
Sent: Tuesday, December 25, 2001 8:36 PM
Subject: Re: PALs (was Re: MITS 2SIO serial chip?)
> I have read it, it's on my bookshelf. PALs were still just
> starting to be seriously used in the very late 70s with an
> increase into the 80s, it was the cost vs board real estate
> vs reliability issue. The testability/reliability issues took
> a few years to gain engineers confidence.
>
> Allison
>
> -----Original Message-----
> From: Pete Turnbull <pete_at_dunnington.u-net.com>
> To: classiccmp_at_classiccmp.org <classiccmp_at_classiccmp.org>
> Date: Tuesday, December 25, 2001 9:05 PM
> Subject: Re: PALs (was Re: MITS 2SIO serial chip?)
>
>
> >On Dec 25, 12:22, Ethan Dicks wrote:
> >> --- ajp166 <ajp166_at_bellatlantic.net> wrote:
> >> > -----Original Message-----
> >> > From: Ben Franchuk <bfranchuk_at_jetnet.ab.ca>
> >> > >> Sure its trivial to do now but we were talking 1981 when PALS
> were
> >> > >> expensive.
> >> >
> >> It depends on what your limited resource is and how costly _that_ is.
> >> ISTR PALs were $2-$10 each c. 1981-1982. If someone remembers
> >differently,
> >> please supply more accurage data. Yes, a single PAL cost more than
> >several
> >> TTL popcorn chips, but given how much you could fold into a single PAL
> in
> >> the way of I/O select logic (a common use on the board I first
> >encountered
> >> PALs on), it wasn't so expensive then.
> >>
> >> > Yes, they were compared to random logic, but if board space was
> costly
> >> > they were cheaper.
> >>
> >> Or if board space was a fixed resource, then it's doubly costly. The
> >> oldest example I can cite from personal experience is the COMBOARD-I
> >> to COMBOARD-II design. Both were early examples of 68000 designs (an
> >> intellegent Unibus serial periperal)... one with SRAM (2114s) and TTL
> >> logic, the other with DRAMs and PALs. One similarity - about 1.5 sq
> ft.
> >> of board space to cram in a CPU, RAM, support logic, a sync serial
> port
> >> (based on the COM5025) a parallel port and Unibus DMA logic.
> >>
> >> In 1981, our designers went with older tech, but the DMA engine was
> >> horribly complicated from the standpoint of the 68000, but it was in
> part
> >> because there wasn't enough room on the board for a better design with
> >> TTL. The second revision (c. 1983-1984) had more onboard I/O, and
> >> implemented the DMA engine as a bank of shared memory to the 68000
> (i.e.,
> >> read/write to a certain range of memory from your code and it
> >automatically
> >> generates a Unibus DMA cycle - most cool). I don't know for a fact,
> but
> >> from what I remember about the designs, I don't think a shared-memory
> DMA
> >> engine would have fit on a Unibus board if it had been made out of
> >popcorn
> >> logic.
> >>
> >> > >I never heard about pal's until about 1990...
> >> >
> >> > PALS are 1970s technology, really old to some of us.
> >>
> >> I didn't see PALs in use until the early 1980s. Yes, I know they came
> >> out in 1978, but products designed with them didn't hit right away.
> >
> >You should read Tracy Kidder's book, The Soul of a New Machine. It
> >describes the design of the Eagle inside Data General from early 1978 to
> >early 1980, and mentions PALs a lot.
> >
> >--
> >Pete Peter Turnbull
> > Network Manager
> > University of York
>
>
Received on Tue Dec 25 2001 - 22:12:09 GMT