View Full Version : 6502 based instrumentation board with 25c32bq eprom

August 23rd, 2014, 07:50 PM
I have an old lab instrument with an embedded micro board based on the 6502. It uses a 27c32bq eprom. I wanted to backup the eprom, and place its contents on another 27c32. I bought 27c32q-35 eproms from ebay. I had trouble programming them with a Willem eprom programmer (pcb3), but finally successeded with a programming pulse of 1ms. When I replace the 27c32bq with my 27c32q, the processor fails to boot, even though Willem verifies a good load. I would think a 35us part should be fast enough. Does anyone know the difference between 27c32bq and 27c32q eproms?

August 24th, 2014, 11:39 PM
I bought 27c32q-35 eproms from ebay.

I would think a 35us part should be fast enough.
That's probably a 350 ns part. It was common to drop the zero off the end. See [here (http://www.jameco.com/1/1/3375-27c32-15-eprom-4k-x-8-150ns-5v-dip-24-memory.html)] for an example.

August 25th, 2014, 01:31 AM
I agree with modem7 that the part you have bought is a 350 ns access time part. The problem is - it may be too slow in returning the data than the one you are replacing.

A random google search for 27c32bq EPROMS turned up -15, -20 and -35 parts (150, 200 and 350 ns access time parts respectively). There must be some additional markings on your original EPROM? Can you double check and report back.

If there are no further markings on your original EPROM - I would suggest purchasing the fastest EPROM you can find (faster than 350 ns) to replace it.


August 25th, 2014, 03:07 AM
I would have thought you need 250ms at the very least, and possibly 120, for a 6502 running at a decent clock speed...

August 25th, 2014, 07:37 AM
What is the 6502 running at (at Phase 0 input)? Is there a dash number on the 6502? The typical 6502 used in the C64, etc. ran at 1 MHz and could use 450 nS EPROM. If you have a rarer 2 MHz 6502 then you need a 250 nS part.

August 26th, 2014, 04:53 AM
I've found problems with some 27C32s and the Willem programmer. The programmer says the part is good and passes verification, but putting the EPROM into a breadboard and manually driving signals shows that 0 bits are higher voltage than they should be. Ie, the programmer is happy, but the processor reading the EPROM sometimes reads a 1 instead of a 0. I ended up wasting a week trying to figure out what was wrong with various parts of the circuit, trying to weed out "bad" EPROMs, etc.

My solution was to slow down the programming cycle to speed 0 instead of the default 2 (silly Windoze interface). Never had a problem since.


August 31st, 2014, 09:41 AM
I'm a bit confused... you have 2532 in the thread title and 2732 in the text... These are 2 different EPROMs with different pinouts and cannot be substituted without wiring up an adapter.