Richard Erlacher wrote:
> I've built CPU's using standard TTL MSI/SSI devices, without any sort of
> microcode, and, since that was in the days before PALs, bipolar PROMs were the
> only handy programmable device that allowed simple localized decoding and
> steering without discarding resources. The fact they can easily provide a
> preset to a cycle counter, based on their inputs even though there might be a
> "sparse" lookup table for that function, saved both time and real estate,
> often rendered PROMs the vehicle of choice.
The main reason I have never played with them is I could never find a
Fuse Prom Burner schematic that looked reasonable. I still would like to
do a TTL computer with fused based proms ( or EEPROM's as modern
substitute )for control logic. I am just finishing up a nice FPGA design
but thinking this is going to be a pain to get a serial prom and have it
burned too. 50,000 sure ! quantity 1, HA-HA you must be kidding.
(EPC1441LC20 altera 440,800 bits -- any place in Canada). While TTL is
low density you don't need to pay $$$ for a license for modern
programiable logic, have the software needed 5+ years down the road! (
That is assuming TTL is still around 10 years from now )
> > The PDP11/05 was 2 full hex-height boards just for the CPU, so around 200
> > chips. It used mostly TTL, but also some PROMs containing the microcode.
> > And the TTL included chips rather more complicated than just gates --
> > things like 16*4 RAMs, 4 bit latches, multiplexers, etc.
This was ball park figures. A 4 bit shift register ,4 bit up counter
,dual 4-1 muliplexer would be the typical ALU parts. I was looking at
74HCXX chips as 74LSXX is harder to find and lots more power. How ever a
74LS382 style alu would be used rather than a 74LS181 if LS parts were
used. A 8 bit x 1 register file is a 8 bit addressable latch and a 8/1
multiplexer. The alu design is for a undefined 24 bit processor with a
classic style of architecture.A PDP-11 has byte operations and a complex
opcode where this architecture would be more PDP-8 style on a single 24
bit word.
--
Ben Franchuk - Dawn * 12/24 bit cpu *
www.jetnet.ab.ca/users/bfranchuk/index.html
Received on Tue Apr 09 2002 - 17:41:04 BST