3 Nov
2001
3 Nov
'01
2:23 a.m.
Chuck McManis wrote:
The above statement is completely untrue. You can get
10 - 100x the "ttl"
equivalent logic in a 44 pin PLCC. Check out the XC9572 some time,
depending on your logic you can replace a whole bunch of TTL and they are
$5.53 each from Digikey, quantity 1. Or go to 84 pin PLCC, still allows you
to do through hole work for $7.00 and get 50% more gates.
That is true but random logic is hard to judge how much will fit in a
FPGA. Normal glue logic often fits well as well as simple I/O devices
like a printer port. It is random state logic, Alu's and memory devices
that don't fit well and that is often what is needed.
Note you can still find the old TTL but you pay a arm and a leg for
them.
A 74LS181 that was $1 in jameco is now $4 here. A 74LS382 is $8.00.
If you need old replacement parts this looks to be the spot.
http://www.rocelec.com/
Note the 74182 is the carry lookahead.
If you're a really lousy logic designer you can
create crap anywhere, no
need to go the FPGA route.
Not in all cases, porting a TTL board to FPGA macros can
take up a
lot of macro cells. The moment you clean up the logic you risk becoming
non portable.
If you use something like the XV1000 (1 MILLION
equivalent gates, then yes
the chip will cost you $1700 and you can design in a complete PDP-11/70,
GT-44 subsystem, RL/RK/RX controllers, SDRAM memory controller, front panel
for blinken lights, full floating point, CIS and EIS instruction sets and a
programmable microstore with about half the damn chip left over.
Four chips are fine -- CPU,I/O and 256Kx16 memory. But ya got have that
front panel!
Makes for a mighty thin RACK mount.:)
--Chuck
Ben franchuk.
PS.Not having used a PDP-11 I could be wrong about the memory.