22 Aug
2002
22 Aug
'02
3:34 p.m.
From: "Eric Smith" <eric(a)brouhaha.com>
Hi
The only issue with PMOS is on the outputs. They
may not pull down as hard as a TTL input pulls up.
This is generally fixed with a pull down resistor
and/or a diode to limit the negative travel. Some
TTL can tolerate some negative on the input, most
CMOS can't ( I think the 4049 can though ).
Dwight
Hmm, but then how is translation done on the
inputs to the ROM? It is
a TTL device feeding the address, so the 0-5v swing (0.5v to 4+v)
swing would appear to be an input swing of +15 to +20.
No translation required. PMOS thresholds are within a few volts of the
positive rail.