Will any 6502 work in a Vic?

SparkyNZ · Post by **SparkyNZ** » Tue Nov 08, 2011 2:00 am

Hi. I just received a broken Vic and by swapping the chips I've determined that the 6502 CPU is dead.

Can somebody please tell me - would any (brand of) 6502 work in a Vic?

Thanks

Post by **joshuadenmark** » Tue Nov 08, 2011 11:43 am

Ive bought one at ebay, was not original but worked fine

http://www.ebay.com/sch/sis.html?_kw=1+ ... 0584473522

Ebay search

SparkyNZ · Post by **SparkyNZ** » Tue Nov 08, 2011 1:06 pm

joshuadenmark wrote:Ive bought one at ebay, was not original but worked fine

http://www.ebay.com/sch/sis.html?_kw=1+ ... 0584473522

Ebay search

Thanks Joshua. I ordered a couple from eBay lastnight. One of the auctions listed that the clone chip was compatible with CBM PET and other 8bit micros so I figured it must be OK. I'll reply to my own posting with the details once I receive the chips. I just wasn't sure if the chips were made with different types of transistors etc (e.g. TTL vs CMOS). I believe the "MOS" name of the CBM 6502 is the company but it scares me into thinkin 'CMOS technology' etc.

Post by **joshuadenmark** » Tue Nov 08, 2011 1:50 pm

Please let us know when your vic is up running.

eslapion · Post by **eslapion** » Tue Nov 08, 2011 4:51 pm

My answer to your original question is no.

I suggest you visit the western design center for advice on compatibility with different versions and manufacturer's implementation of the 6502.

Some are CMOS, some are NMOS, some support DMA, most don't.

matsondawson · Post by **matsondawson** » Tue Nov 08, 2011 5:06 pm

I think the overflow pin on the WDC one is different, and you have to make a slight change to get it to work.
Not to mention the loss of illegal instructions.

ruud · Post by **ruud** » Sat Nov 12, 2011 2:57 pm

eslapion wrote:My answer to your original question is no.

I have to contradict this. If no illegal codes are used, all 6502 variants should work. When using my hardware debugger, I often replace the original 6502 by a WDC 65SC02 ot be able to see what is going on when the 6502 writes data to the bus.

And FYI: you can even use a 65816 but then you have to do a bit of soldering: http://www.baltissen.org/newhtm/02to816.htm.

eslapion · Post by **eslapion** » Sun Nov 13, 2011 7:59 am

ruud wrote:
eslapion wrote:My answer to your original question is no.
I have to contradict this. If no illegal codes are used, all 6502 variants should work.

If used as is, the W65C02S WILL cause a short circuit on pin1.

This variant of the processor also supports external bus control and DMA. The original 6502 does not.

RJBowman · Post by **RJBowman** » Sun Nov 13, 2011 11:35 pm

The so-called undocumented opcodes may not work on some clone chips. I don't know how widely used these opcodes are.

GreyGhost · Post by **GreyGhost** » Tue Nov 15, 2011 5:11 pm

If I understood correctly, even some of the standard opcodes act differently on different 6502's, with the setting of flags. You might end up with some programs needing modification.

Mike · Post by **Mike** » Wed Nov 16, 2011 2:14 am

GreyGhost wrote:even some of the standard opcodes act differently on different 6502's, with the setting of flags.

The CMOS variant of the 6502 fixed some bugs in the arithmetic instructions, after an ADC or SBC in decimal mode the N and V flag were unusable on the NMOS 6502 (they reflected the binary result). Furthermore, the D flag is cleared after a reset, and several page-related ideosyncracies, like missing page increments in ZP-(indirect)-indexed and indirect JMP, were fixed.

Nothing special to be concerned of, though. You'd avoid these cases on a NMOS 6502. Only problem might be when you'd use the fixed versions on a 65C02, and then try them on a 6502 and then ran into these cases by accident - that might give you a longer debugging session.

RJBowman wrote:I don't know how widely used these opcodes are.

Some time ago we had a similar discussion about the usefulness of the undocumented instructions, leading to the thread '65xx Opcode statistics, an example'.

Greetings,

Michael

SparkyNZ · Post by **SparkyNZ** » Sat Dec 10, 2011 1:00 pm

Hi Everybody. Just to recap on my original post.. I received my new chips yesterday. They're CM630P chips. I plugged it in and the Vic is working great again. Ran a few demos and games OK so thats good enough for me!

Post by **joshuadenmark** » Sat Dec 10, 2011 2:00 pm

Great

one more vic waked up from the dead.

eslapion · Post by **eslapion** » Sat Dec 10, 2011 2:24 pm

SparkyNZ wrote:Hi Everybody. Just to recap on my original post.. I received my new chips yesterday. They're CM630P chips. I plugged it in and the Vic is working great again. Ran a few demos and games OK so thats good enough for me!

The W65C02S caused problems when loading and saving data to datasette and floppy drives.

If these worked fine with your chips then everything should be ok.