4 Jan
2004
4 Jan
'04
5:10 p.m.
Tony are you talking about the old schul logic?
ed sharpe
----- Original Message -----
From: "Tony Duell" <ard(a)p850ug1.demon.co.uk>
To: <cctalk(a)classiccmp.org>
Sent: Sunday, January 04, 2004 9:45 PM
Subject: Re: Iomec disc drive?
> The DTL already tripped me up once. I had a J/K
flip flop with both Q
and
> -Q low. Turns out -Q was wired with the output
of another gate as an
> apparent ECO (wasn't on the schematic). Sigh. At least with TTL you
have
> the clue of the part being open-collector to help
you realize someone
did
that. 8^)
Years ago I was working on a thing called a 'Solatron DTU', which was
basically a data logger add-on for a DVM (it had a 20 channel input
multiplexer, a real time clock, and output boards for a Facit 4070 punch
and an ASR33 IIRC). Anyway, it wa all DTL inside.
I found a (genuinely) dead JK flip-flop. Found the pinouts from the
schematics (which fortunately I have), and thought I'd found a
pin-compatible TTL replacement. Popped it in, and the darn thing still
didn't work. No, it wasn't a wire-AND connection... It turns out that the
DTL and TTL chips have the same pinout _except_ that Q and Q/ are swapped
round, and that was easy to miss when looking at the databooks.....
-tony