8 Jul
2001
8 Jul
'01
9:07 a.m.
A big part of the question would be whether the devices failed permanently, or
just failed in that particular application. Hard failures with respect to
address lines were common, and there were popularly distributed memory tests
just for that sort of failure.
I often ran into failures, not only with 2114's but in general, that didn't
persist in a given device, and where replacement with another new or presumed
healthy device would, eventually produce the same failure mode. I didn't
attribute this sort of thing to device failure, however.
It's pretty easy to develop the opinion that this device or that is more prone
to failure than some other. I was convinced for a time that 'LS244's had an
abnormally high failure risk associated with them, likewise, 1489's. However,
it's often the way in which they're used, in these examples, certainly, that
makes the difference, as both devices were often used in connection with
external cables and equipment.
Have you any examples of how you determined that there was an addressing
failure? Was an address input shorted to some other line or supply on the 2114?
I've seen that sort of thing happen with other memory devices, so it's certainly
conceivable with these as well.
The main problems I've run into myself have related to address-setup-to-nWE and
data-valid-to-nWE rising edge, as well as write-data hold times, (often violated
with 6502 and 68xx processors, BTW) which clearly is an application error and
not a device failure. The relationship between nCS, nOE, and nWE to the
settling of addresses and data can be pretty touchy in tightly timed circuits
such as those used for sharing memory between a microprocessor and a video
refresh logic set. That was one pretty common application in which I saw them
fall down. I bought a bunch of Intersil 7114-HCC types (70 ns, so, MUCH faster
than was normally required of 2114's) just to prove that a circuit was badly
designed for the desired memory speed (memory speed determined cost, and cost
targets were often paramount). The problems often went away with the faster
RAM.
Dick
----- Original Message -----
From: "Tony Duell" <ard(a)p850ug1.demon.co.uk>
To: <classiccmp(a)classiccmp.org>
Sent: Sunday, July 08, 2001 12:05 PM
Subject: Re: Lack of robustness with 1K and 4K RAM chips (was Re: 2116 and other
old memory chips)
>
> While 2114's weren't the only common I/O SRAMs, they were the first in
really
<snip>
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.
I don't think the problems I've exeprienced with 2114s are due to misuse.
For one thing, the chips worked fine for several years (i.e. they didn't
fail a few minutes/hours after swtich-on). The replacements also worked fine.
Most of the faults I've had have been addressing errors. One address line
does nothing (so data written to 1 location shows up somewhere else). I
can accept that violating the timing specs could cause
contention between the output buffers in the 2114 and system data bus
drivers. But if it did any damage, it would most likely cook one of the
data output buffers in the 2114. Not an address input.
-tony