6502.org

Yes.

Hmm - at least datasheet of my NMOS 6509 says it wants to have a full rail clock. (It actually seems to work w/ TTL level clock.) Is your circuit only for CMOS CPUs or is it also intended for NMOS w/ full rail clock?

(I note that the 6502 launched at a 20% price premium for including the on-chip clock generator. The 8080 needs a 9V clock... clocking was hugely inconvenient prior to the 6502.)

The 74AC74 flip-flop can swing Q and /Q from Vcc to ground and source or sink up to 24 ma. It should work fine with the 6509. You could also use a 74ABT74 instead of the 'AC74 to get more drive, but that's probably not necessary in your application.

Incidentally, if you need a Ø1 output along with Ø2 you can derive the former from the /Q pin on the flop. Ø1 and Ø2 will be exactly 180 degrees out of phase with each other.

I agree with BDD that AC series parts are an excellent choice for a clock circuit. But the 6509 is an odd bird, unlike other 65xx CPUs in that it requires two separate, non-overlapping clocks -- at least that's what the datasheet says. (The 6800 is like that, too, IIRC).

Somewhere I saw the clock circuit for the CBM-II (?), which is a 6509 machine. It used two TTL logic gates cross-coupled in a manner that avoids overlap, and low-value pullup resistors to ensure adequate logic-high voltage levels. I suggest you adopt the same circuit, but using 74AC (and omitting the pullups).

-- Jeff

Right, forgot about the weird clock requirements, which are clearly shown on the timing diagram (attached).

Till now I use a SN74ALS02N... let's see what's in my storage box... *rummaging through arsenal*... hmmm... ...I even don't have another '02 of any kind... so the ALS will have to do.... and I should add the pull-ups then.
You probably mean CBM-500 and CBM-6xx or "b-model": http://www.zimmers.net/anonftp/pub/cbm/ ... index.html
It uses 2xNOR to generate the non-overlapping clock. I copied my clock circuit from there (but somehow the resistors didn't make it to my breadboard...)

Right, thanks -- this is the part I remember (from this page).

Pin 13 and pin 10 of the 'S02 NOR drive Φ1 and Φ2. And the cross coupling guarantees the "non-overlapping" behavior. Pin 13 must finish going low before pin 10 can go high, and vice versa.