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vbriel
 Post subject: Internal clock on 6502
PostPosted: Wed Sep 06, 2006 1:50 am 
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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

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GARTHWILSON
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PostPosted: Wed Sep 06, 2006 4:30 am 
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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.
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8BIT
PostPosted: Wed Sep 06, 2006 4:50 am 
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Location: Sacramento, CA
vbriel wrote:
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)

Quote:
Crystal or RC network will oscillate when
connected between PHI2 and PHI10.

where PHI2= pin 37 and PHI1O= pin 3

Hope that helps.

Daryl
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vbriel
 Post subject:
PostPosted: Wed Dec 27, 2006 4:29 am 
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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

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