7 Jul
2001
7 Jul
'01
12:31 p.m.
While 2114's weren't the only common I/O SRAMs, they were the first in really
broad usage. I'd guess that the reason for so many problems associated with
them was that it took a while for people to figure out how to use common I/O
devices in fairly tightly timed circuits such as shared video refresh memory in
a microprocessor-based system. The timing looked quite simple, but between
setup and hold time restrictions and the correct timing of the nWE line, it was
pretty easy for folks to get into contention problems. I suspect that was a
pretty significant factor in the frequency of malfunction with these devices.
They were really popular in video games, many of which weren't terribly well
designed, since that would have run up their cost. They were popular, though,
because they took up less space than an equvalent number of 2102's, which had
separate data in and out.
As for failures, I don't remember lots of trouble with them. I suspect that
they were easier to use, and hence, less prone to misuse, in systems with a
single write line rather than a write and a read, however.
Dick
----- Original Message -----
From: "Tony Duell" <ard(a)p850ug1.demon.co.uk>
To: <classiccmp(a)classiccmp.org>
Sent: Saturday, July 07, 2001 12:34 PM
Subject: Re: Lack of robustness with 1K and 4K RAM chips (was Re: 2116 and other
old memory chips)
> While I don't dispute Tony's experience,
mine has been somewhat different.
I've
My comments (about the unreliability of 2114s) are not based on a real
scientific survey. It's just that I have had an excessive number of 2114s
fail. The most recent case was an HP82163 HPIL video interface. It was
working a few months back, I tried it again and got some garbled
characters. Writing to one position on the screen would sometimes cause
another character elswehere on the screen to be changed.
It looked like an addressing error for the top 4 bits of video memory.
There was a pattern to the corruption -- the corrupted character would
have the bottom 4 bits left alone, but the top 4 bits sent to the same
states as those for the character you'd just written.
It was either a very obscure fault in the HP-custom video chip, or a
video RAM playing up. The video RAMs were 1K*4 devices, 18pin DIL, with
HP numbers. But they were really 2114s. I changed one of them (for once I
picked the right one first time), and the unit worked again.
It's got to the point, I am afraid, where if I see a board with 2114s on
it, and the fault could well be RAM-related, then I test an/or change the
2114s.
I have had other RAM fail. A DEC LA324 where all the SRAM chips (I think
it's 2 32K*8 and 1 8K*8 one) failed at once. And I've had the odd 4116 or
4164 die. But they seem to be more reliable than 2114s...
> If one uses only 1000 or so part per week, one doesn't get a complete
picture of
> the real failure rates of memory devices, if you
test 40 boards at a time,
each
Very true.
However, I'll still suspect 2114s if the fault can be memory-related :-)
-tony