Re: PLA replacement

From: Rob Clarke <>
Date: Sat, 01 Dec 2012 17:54:00 +0100
Message-ID: <>
It's a hotly debated subject on the mainstream C= forums and there's an 
enormously long thread on Denial, which is odd as the VIC didn't have a 
PLA, that discusses the pro's and con's of PROM based PLA's:

I just bought 25 x M27C512-90B6, which appears to be the EPROM of choice 
for PLA replacements, specifically to make ones for my P500 and 8296. 
I'll report back when I've had a play, although it'll be after Christmas 


On 01/12/2012 17:43, wrote:
> On 2012-11-27, at 19:22, Gerrit Heitsch wrote:
>> An EPROM PLA can work, with the right EPROM (which is not necessarily the fastest you can get), but most of them fail with modules like EasyFlash.
> Now that's a bad news indeed. I hoped for something easy (like EPROM) but reliable.
>> As for the timing... grab the datasheet for the 82S100 or the Fairchild 93459PC from the net. That's the original bipolar PLA. Its spec is 45ns, the fastest EPROM I have ever seen was a 27C256-55, but as I said, speed isn't everything.
>> So far I have enough real PLAs that I didn't have to resort to using an EPROM PLA.
> It is not a question of having the PLAs. I have them too. And despite the bad press it's been receiving for years, I haven't seen many of them failing over the years. The objective of all this activity though is to replace as many custom parts as possible with generic and widely available ones. But for me it is not enough that it would work in "most cases". It has to work at least as good as original design. That has to include things like EasyFlash (IDE64, 1764, you name it) use cases too. If EPROM is no good here (and not because of speed!), then it is no good at all. Which in turn means a sort of CPLD would be needed again..

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Received on 2012-12-01 17:00:36

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