Maybe you all knew this already...
Posted: Sun Oct 27, 2013 12:45 am
I always wanted an easy way to detect wether a VIC-20 has an original NMOS 6502 or a newer 65C02 inside.
Here's what I found in wikipedia:
Here's what I found in wikipedia:
Easy enough...The 6502's memory indirect jump instruction, JMP (<address>), is partially broken. If <address> is hex xxFF (i.e., any word ending in FF), the processor will not jump to the address stored in xxFF and xxFF+1 as expected, but rather the one defined by xxFF and xx00 (for example, JMP ($10FF) would jump to the address stored in 10FF and 1000, instead of the one stored in 10FF and 1100). This defect continued through the entire NMOS line, but was corrected in the CMOS derivatives.