RE: Synertek 6502 compatibility

From: Bil Herd <>
Date: Sat, 14 Apr 2012 13:23:50 -0400
Message-ID: <>
Yup supposed to be compatible.  Make sure you have the same speed grades.
If you have a scope take it around the pins and make sure everything look
right or at least similar from pin to pin. (go from ground to 4.75volts,
only stops at other voltages when floating.

Now the interesting thing is that your number is returned as floating
point.  Somehow that makes me think that there may have been a mask
stepping where some bug with overflows or dec math or something may have
been fixed.

-----Original Message-----
[] On Behalf Of Rob Clarke
Sent: Tuesday, April 10, 2012 6:42 PM
Subject: Synertek 6502 compatibility

Hello gentlemen,

Does anyone know if the Synertek 6502 is 100% compatible with its MOS
cousin? I have one which I tried in an otherwise working PET and I get
"31653.4784 BYTES FREE" instead of 31743, which is 89.5216 bytes short :-/

I know some of the later CMOS incarnations did not have the same behaviour
with undefined op-codes but a) this a 1984 chip and b) I can't believe the
PET kernal would use them anyway.

It is also possible that this chip is just duff of course.


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Received on 2012-04-14 18:00:04

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