Char-ROM replacement

From: Gerrit Heitsch <>
Date: Thu, 20 Sep 2012 19:00:36 +0200
Message-ID: <>

since I had a C64 char ROM (901225-01) go bad this year, I was looking 
for a replacement. The pinout of the ROM matches the 2532 EPROM, but the 
only one I had was 450ns and that's too slow. I tried it, but all I got 
was a snow storm at power up.

Then I found a few TMS2532-30 on ebay and got around to try 2 of them 
today. Those are fast enough, you get the expected picture at power up.

So, we have a verified drop-in replacement for the char ROM. The 2532 is 
NMOS so it will get warm, but you don't need any adapter, just program 
it, and plug it into the socket.

I also wanted to see how a ROM and the EPROM behave and used to the 
scope to look at the time between _CS going LOW and the state change on 
D0, showing me data being ready. The ROM did that in about 50ns! The 
2532-30 took about 150ns. Quite a bit faster than the expected 300ns. 
Did TI just test for 300ns as highest speed back then and never bothered 
to see if any were faster?

Oh, and there is a 2532A too, available in 250ns, but needs a Vpp of 21V 
instead of 25V. At least my programmer can't do that combination.


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Received on 2012-09-20 18:00:04

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