--- 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.
The technology is 1970s, but the products are, for the most part, 1980s.
-ethan
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Received on Tue Dec 25 2001 - 14:22:36 GMT