Address Decoding

kc5tja · Post by **kc5tja** » Mon Aug 24, 2009 2:28 pm

Don't tell Robert Grossblatt that, who in his 8088 Project Book, used an EPROM for address decoding with his 4.77MHz 8088 computer. Build on breadboards no less.

The trick to using EPROM for such things is to make sure you have a fast-enough part.

BigDumbDinosaur · Post by **BigDumbDinosaur** » Tue Aug 25, 2009 12:34 am

You can get some pretty fast EPROMs these days. For example, ST Micro's M27C256B has a 45ns access time. It's a 32Kbx8, UV-erasable part and probably would work fine as an address decoder.

Post by **Mike Naberezny** » Tue Aug 25, 2009 5:26 am

BigDumbDinosaur wrote:

You can get some pretty fast EPROMs these days. For example, ST Micro's M27C256B has a 45ns access time. It's a 32Kbx8, UV-erasable part and probably would work fine as an address decoder.

Some Commodore computers use a Signetics 82S100 FPLA. This chip is no longer produced and is not supported by many device programmers. A few people have made replacements using a fast EPROM on a small adapter. I have also tried this and have had success with the AM27C512-45. From my reading of the datasheets for both parts, the timing characteristics are similar.

Regards,
Mike

BigDumbDinosaur · Post by **BigDumbDinosaur** » Thu Aug 27, 2009 4:13 am

Mike Naberezny wrote:

Some Commodore computers use a Signetics 82S100 FPLA. This chip is no longer produced and is not supported by many device programmers. A few people have made replacements using a fast EPROM on a small adapter. I have also tried this and have had success with the AM27C512-45. From my reading of the datasheets for both parts, the timing characteristics are similar.

Regards,
Mike

I would think that the timing requirements for any Commodore 8 bit unit would be easily accommodated. After all, we're talking about a 1 MHz clock, hardly a strain on today's silicon. A 45ns EPROM wouldn't even work up a sweat in such an application.