Can I replace a 6502B with a 6502C (SALLY), not other changes?

[ACML]

I know you can't go the reverse direction. You can't just drop in a 6502B into a 1200XL, but my question is can you drop in a 6502C into an Atari 800 CPU board that had a 6502B? Will it work with no further modifications? My situation is that I have an older 800 CPU board with a bad 6502B. The CPU board has the extra four support ICs since the 6502B does not have the HALT feature. I have no spare 6502Bs, but I do have a spare 6502C (SALLY). If I put the 6502C in the 800, will it work fine and just ignore the HALT feature of the "C". I think its plausible since the older CPU card doesn't use the pin on the "C" for HALT. Anyone try this yet?

 

[Rybags]

I think you probably can but I'm getting conflicting info re the R/W pin.

 

Sally uses pin 36, docs I have for 6502 have it at pin 34. Jindroush's Atari schematic of the older 800 CPU board has it pin 36.

It should be easy enough to work out what pin your board expects it to be.

 

Re the cycle holding stuff - Sally supposedly does internally what the discrete logic chips do externally probably with a little less latency but I don't see why a swap shouldn't work (of course it'd revert to the external cycle control circuitry).

 

 

ed - you might need to connect the /HALT pin on Sally to a pullup since it's active low.

Edited January 6, 2018 by Rybags

[guus.assmann]

Hello,

You do need to tie the /Halt line high with a Pull-up.

And the R/w is on a different pin.

For the rest, the Sally-CPU will work fine in an old 800 board. (I've used it in various other boards)

Also, it's not a big problem to buy a 6502. And a 65C02 is also available.

Just compare the schematics to find out the pin numbers.

[ACML]

Thanks Rybags and guus.assmann,

 

I'd like the repair clean, so I'll just order another 6502B (they are only $7). Thanks for the tech info!!