65C02 replacements don't work

Sonny · Post by **Sonny** » Fri Aug 29, 2008 1:46 pm

Hello,

I have a broken chess computer running on a Ricoh RP65C02G. I replaced the CPU with another of exactly the same type, and it worked.
So I've ordered some spare CPUs of the type WDC65C02S6TPG-14, and all 3 of them don't work. Did I miss any compatibility items there?

Thanks for any help!

Thomas

Lost · Post by **Lost** » Fri Aug 29, 2008 3:49 pm

My (admittedly limited) understanding of the compatibility issues with using the W65C02 chips is 2 things...

First, the current WDC 65c02 does not implement any of the unofficial op-codes. So, if your system is making use of undocumented op-codes from your specific chip, you may find problems.

Second, the WDC 65c02 may have quicker transition time requirements than your old board provides. The timing isn't too bad but it is build to run at 14MHz and the transition time requirements reflect that. Of course I've got one running on a solderless breadboard at 2MHz without a problem.

GARTHWILSON · Post by **GARTHWILSON** » Fri Aug 29, 2008 4:42 pm

It looks like the Ricoh processor is also CMOS which did not have the undocumented op codes, so that part should be irrelevant. I don't find a data sheet for it online for it. Does one exist? One possible factor is the pin differences. The WDC processor has bus-enable (BE) on pin 36 which needs to be high. Does your board pull it down? Pin 36 was NC on previous 65c02's. The WDC processor has a very weak internal pull-up on 36, so weak that contamination on the board could be pulling it down.

8BIT · Post by **8BIT** » Fri Aug 29, 2008 6:21 pm

Also, most 6502 & 65c02's have a ground input on pin 1, while the WDC 65c02 uses it as an output. You can bend the leg of the IC out so it doesn't go into the socket's hole. Your system won't need to use the output on pin 1.

Does your board use a TTL oscillator or is it using a crystal and glue logic to drive the clock? As stated earlier, the WDC requires a fast rise and fall time on the clock.

What test equipment do you have available?

Daryl

Sonny · Post by **Sonny** » Fri Aug 29, 2008 9:09 pm

GARTHWILSON wrote:

The WDC processor has bus-enable (BE) on pin 36 which needs to be high. Does your board pull it down? Pin 36 was NC on previous 65c02's. The WDC processor has a very weak internal pull-up on 36, so weak that contamination on the board could be pulling it down.

Hello,

thank you so much, you solved my problem. I tried to repair a vintage chess computer (from 1984) running at 3.7MHz, and its processor was definitely dead; when I replaced it with another old 65C02 the computer worked. Since I needed this replacement processor for another computer I bought some new WDC65C02.

Pin 36 of the 65C02 was not connected on the board. I soldered a pull-up resistor between VDD and BE, and now it works.

Thanks again to all who replied to my post.

Thomas.