Re: HC logic with 6502+rigging up a crystal

[ralphp@gcstation.net (Ralph Wade Phillips)]

Hi, Rob!

In article <515o1r$4p4@totara.its.vuw.ac.nz>, Rob Thomson
<rob.thomson@vuw.ac.nz> wrote:

> Hi,
> 
> Can I use a NMOS 6502 or 6522 happily with 74HC CMOS logic?

        Sure!  The Apple ][ family had a LOT of 74 and 74S and 74LS logic
strung off of the 6502.  You can also use the HCT family for even better
compatibility.

> 
> Also, what is the best way to get from up a 4Mhz crystal to two
> opposite 1Mhz signals. eg. what capacitors, resistors and logic
> (latches or counters?) would I need to do this and how.
> Is it easier to get a 1Mhz crystal and invert it somehow (how?)
> to get these two opposite 1Mhz signals.

        Well, I'd take a 74LS92 or 'LS93, and use the /4 section.  The
output can then be feed to an inverter (74HCT04 or 74HCT14 come to mind)
to reverse the phase.

        Another way would be to use a 74HCT74, and use the Q output of the
first  section to drive the clock for the second one, and then you can use
the Q and /Q outputs for your two signals.  This has always given me more
fits than a '93 or '92 does, however ... <B-)

> These signals would be going straight to a 6502 and 6522.
> 

        Feed the output of one of the /4 sections of a '93 to one
inverter, and feed its output to both a) a SECOND inverter and b) the
Phase 0 input of the 6502/6522, and take the output of the SECOND inverter
for Phase 2, and you've got your clock!

        RwP

> Thanks for any help,
> 
> Rob.

-- 
Ralph Wade Phillips, CET #LA-82
ralphp@gcstation.net