21 Nov
2001
21 Nov
'01
9:42 a.m.
Just how fast do these devices have to be, and how deep are they? I've got some
35ns 8kx8 CMOS EPROMs, in skinny DIP packages, and I'd imagine that other
configurations are out there as well. These are contemporaries of the 25ns
22V10 UV-erasable PALs from CYPRESS. That would date them about 1990.
Small bipolar PROMs were often used like PALs, which were not yet popular, or
were more expensive than the PROMs. I've not seen EPROMs that small, however,
but it's likely a big EPROM would work if it's fast enough. In a case where the
PROM is a logic element rather than a program store, a PAL could well be
substituted.
Dick
----- Original Message -----
From: "Tony Duell" <ard(a)p850ug1.demon.co.uk>
To: <classiccmp(a)classiccmp.org>
Sent: Wednesday, November 21, 2001 1:35 PM
Subject: Re: I'm guessing you have solved this problem...
Hi Tony,
Presumably this is directed at me?
What have you used to replace the various DEC bipolar ROMs in an 11/45
CPU?
I've never had to replace one. If I did, I'd try to get a similar bipolar
PROM from any manufacturer (there are still quite a number around, even
if they're not being made) and program it from the tables in the
printset.
Other than that, I'm not sure. This sort of logic is not going to fit
well into an FPGA or CPLD, I think. Are there fast enough EPROMS now (I'm
out of touch with the latest devices, but I think I remember seeing some
fairly fast devices in the databooks).
-tony