Posted By
JamesC
on 2003-04-16
|  6510 vs 7501/8501
The 6510 uses bytes 0 and 1 as on-processor data driection registers. This is why programs on the C64 will have a POKE 1,53 (or something similar) when the program needs to bank out the BASIC or KERNAL ROMs.
On the 264 series, we bank out BASIC or the KERNAL by writing to the data direction registers on TED ($FF3E and $FF3F). The on-processor data direction registers on the 7501/8501 aren't documented well enough for us to muck with them directly.
If the 7501 were 100% backward compatiable with the 6510 then it would share the same numbering sequence (6515 maybe) before jumping up to the 75xx series.
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