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Internal clock on 6502
Posted: Wed Sep 06, 2006 1:50 am
by vbriel
While doing some research on an old SBC I noticed that it used the internal clock option on the 6502. Does anybody have any info on resistor/cap values to use for this setup? Has anybody done this?
Vince
Posted: Wed Sep 06, 2006 4:30 am
by GARTHWILSON
Sure. One I've been using frequently has a 5.6K from pin 3 to pin 37 of the DIP, and a 76pF (56pF + 20pF in parallel) from pin 37 to pin 39. This gives about 900kHz. A product we sold a lot of uses 68pF instead of 76pF, giving about 1MHz. I haven't tried to see how high you can go in frequency doing it this way. You can also put a crystal directly on the pins. The method is in the data sheet. This is not recommended for the higher clock rates, but works fine at a MHz or two.
Re: Internal clock on 6502
Posted: Wed Sep 06, 2006 4:50 am
by 8BIT
While doing some research on an old SBC I noticed that it used the internal clock option on the 6502. Does anybody have any info on resistor/cap values to use for this setup? Has anybody done this?
Vince
Vince,
The only reference I could find for using an RC network was in the WDC 65C02 datasheet under the caviots section (towards the rear)
Crystal or RC network will oscillate when
connected between PHI2 and PHI10.
where PHI2= pin 37 and PHI1O= pin 3
Hope that helps.
Daryl
Posted: Wed Dec 27, 2006 4:29 am
by vbriel
Hey Daryl, thanks for the info. Actually, I have hi-res scans of an old OSI-300 SBC that uses this setup. I'm going to reverse engineer it from the photo's (not that easy).
Vince