the CPU replacement that use a selected 6502 N-MOS core: it manage the illegal opcodes.
The CPU4C16, specific for the C16 board shape:
Features:
A) normal sw N-MOS 6502 behaviour (as 8501, illegal opcode included)
B) The I/O bits are at right places: the self-turbo routines (loaders) will work
C) R/W line is put on 3state and HOLD as 8501 timings spec
D) TBC (Time Base Corrector) technique applied to help the CPU, also into the "worst case", for matching the correct bus timings
E) each 6502 (included) are selected for 2 specs:
---1) it has to be an N-Mos,
---2) it has to match to the specifics bus timings
Remember that N-MOS 6502 chips are discontinued,
often on market the sold chips are refurbished and relabelled with a label different to the old one:
chips marked as "6502" may not be N-Mos as it have to be, and vice versa (C-MOS, so no execution of the illegal opcode).
I found a chip labelled as "W65C02S" (10MHz C-MOS) that is a 1MHz N-MOS, and some of not working chips marked as "MOS6502A" seem to be MC6809 Cpu...
More details: http://www.amibay.com/showthread.php?10 ... n-progress
On sale on Amibay: http://www.amibay.com/showthread.php?11 ... CPU4PLUS4)