TTL computing

From: Richard Erlacher <edick_at_idcomm.com>
Date: Sun Apr 14 23:13:28 2002

That doesn't seem to me as a failure of the 2114, but, more likely, a failure
in the update logic in the refresh memory circuit, possibly in a buffer enable
or a shortage of hold timing on the data with respect to the write line.
What, exactly, do you mean by "dud" character? If it appears exactly in the
middle of a 2Kx8 memory array, it could, indeed be a stuck bit, and if it runs
from the middle to the top/bottom that would be a candidate for a failed
memory bit also. If, however, it moves horizontally, or moves outside the
range residing in a single device, it's clearly something else. Have you
tried moving the device around in the video memory array? It seems to me that
there have to be at least two of them, and the "dud" character, whatever that
is, should follow the device.

2114's are just about as plentiful as any device of the era could be. You
should not have a problem replacing it. I don't know what the problems of
sending hardware from the U.S. to the U.K. are, but I'm willing to send you a
handful if you figure out how.

The 2114 was about the first common I/O RAM device to achieve major
popularity, though there were others, and it took people a while to figure out
how to time things. A lot of such applications, particularly if they relied
on the write timing of 680x or 650x CPU's didn't provide enough hold time on
the data. One fix on a 6502 was to time write cycles with phase-0 (the input
clock) while using phase-2 for gating the reads. It may work similarly on
other CPU's as it increases the data hold time after a write.

Dick

----- Original Message -----
From: "John Honniball" <coredump_at_gifford.co.uk>
To: <classiccmp_at_classiccmp.org>
Sent: Sunday, April 14, 2002 4:42 PM
Subject: Re: TTL computing


>
> Tony Duell wrote:
> > > > I've had semicondcutor RAM fail, albeit not DRAM in a PC. 2114s are
> > > > particularly bad for this.
> ...
> > Hmm.. I've had so many 2114s fail, in equipment from different
> > manufacturers (examples : a Commodore 8050 disk drive, a TRS80 Model 3
> > (video RAM) and an HP82163 video interface) that I really suspect the
> > chips...
>
> I had a 2114 go bad in my UK101. I swapped it into the video RAM,
> which made the stuck "1" bit visible as a dud character in the
> middle of the screen. Scrolling made it "smear" all the way up
> to the top.
>
> More recently, I've managed to obtain a supply of 2114s to
> (hopefully) keep the UK101 going.
>
> --
> John Honniball
> coredump_at_gifford.co.uk
>
>
>
Received on Sun Apr 14 2002 - 23:13:28 BST