Substituting 65C22 for VIC's VIAs

[Richardc64]

Years ago an internet friend told me he substituted a 65C22 for one of the VIC's VIAs and said it worked in one socket but not in the other. I don't remember which socket he said was the one that caused problems, and after all this time doubt if he would remember either, even if I knew how to contact him.

Has anyone had any exprience relevant to this question?

Thanks in advance.

[eslapion]

A few years ago, I mentioned the Rockwell 65C22 is NOT a good replacement to the good old MOS 6522 because it has a totem pole output on IRQ B. The real MOS 6522 has an open collector output on that pin making it compatible with multiple circuits connected together.

The correct replacement for the MOS 6522 is the W65C22N from Western Design Center (available from Mouser). Apparently, people don't catch on much... or don't care as I've been saying this everywhere I can. Here and Amibay, at least.

Back in 2015, I have CMOSed one of my 1541 drives (R65C02 and 2 W65C22N) and it's now my 'coolest' Commodore disk drive and I mean this in the thermal sense of the word.

See:
http://www.westerndesigncenter.com/wdc/w65c22-chip.cfm
Pay attention to W65C22S/W65C22N Differences at the bottom of the page

https://www.mouser.com/
Search for W65C22N6TPG-14

[Richardc64]

Thank you. That was very informative. Doesn't solve the mystery of which socket my long-lost-friend's 65C22 worked in and which it didn't, but since the chip I have isn't WD I don't think I'll try it in either VIA socket.

Thanks again

[eslapion]

Thank you. That was very informative. Doesn't solve the mystery of which socket my long-lost-friend's 65C22 worked in and which it didn't, but since the chip I have isn't WD I don't think I'll try it in either VIA socket.

Thanks again

You are welcome.

IRQB (aka IRQ!) is pin 21 and looking at the VIC-20 schematics, this pin is shared in the same manner, one of them on the IRQ bus and the other on the NMI bus. This means you shouldn't use a VIA with a totem pole output on either of them.

You don't have to have a WDC (that's Western Design Center, NOT Western Digital) to have a good replacement chip. In fact, WDC also sells the W65C22S which is exactly like Rockwell's R65C22. Both of which are CMOS and with the unwanted totem pole output.

Rockwell also made and sold the R6522 which is NOT CMOS and IS compatible with Commodore computers and drives. You can easily find them on eBay for a relatively low price but DO NOT buy anything from China as these are usually hoax chips.

The W65C22N is the only new and currently still in production correct replacement for legacy NMOS technology 6522 chips, hence the N suffix. They usually sell for less than legacy MOS 6522 or R6522 (the real ones, not the Chinese frauds) you can find on eBay. You can get them from Mouser as indicated above but they can also be found on eBay -> see item 163550576874

I find them amazing because they don't have the problematic totem pole output but they are made with CMOS fabrication process and they consume less than a tenth the power of the original MOS 6522 chips so they don't heat at all.