Re: HC logic with 6502+rigging up a crystal

[verdini@galileo.pi.infn.it (Piero Giorgio VERDINI)]

Tilghman Lesher (lesherjt@vuse.vanderbilt.edu) wrote:
: Nathan Mates (nathan@visi.com) wrote:
: : In article <515o1r$4p4@totara.its.vuw.ac.nz>,
: : Rob Thomson  <rob.thomson@vuw.ac.nz> wrote:
: : >Can I use a NMOS 6502 or 6522 happily with 74HC CMOS logic?

: :    Should be able to do so pretty easily. The Apple I and II had a
: : heck of a lot of 74xxs onboard. (Wish I had a schematic or motherboard
While I have nothing to comment on the chip selection, I think I
should warn people from using 74HC-series chips directly connected
to 74-non-HC outputs - the HC stuff expects 0V for a logical 0 and
5V for a logical 1, whereas TTL logic only guarantees less than 0.8
Volts for a 0 and at least 2.4-2.8 (depends on the family) Volts
for a 1 - which can send the HC input CMOS transistors into HEAVY
conduction (since the basic CMOS gate is an inverter obtained as a 
high-gain inverting apmlifier...). HCT logic however will accept
TTL input levels (Highspeed Cmos Ttlcompatible...) and provide good
saturated CMOS levels for further layers of HC gates. Regards,

--
				Piero Giorgio Verdini
				Research Physicist
				Sezione I.N.F.N. di Pisa