PALs (was Re: MITS 2SIO serial chip?)

From: Pete Turnbull <>
Date: Tue Dec 25 19:25:12 2001

On Dec 25, 12:22, Ethan Dicks wrote:
> --- ajp166 <> wrote:
> > -----Original Message-----
> > From: Ben Franchuk <>
> > >> 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
> please supply more accurage data. Yes, a single PAL cost more than
> 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
> 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
> 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
> 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 - 19:25:12 GMT

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