Logic Analysers

dwight dkelvey at hotmail.com
Fri Feb 3 17:29:51 CST 2017


 What you see on the other select line is what is called a glitch.

These are not that uncommon during the early part of the address.

What is important is that there are no glitchs when ALE transitions.


From: cctalk <cctalk-bounces at classiccmp.org> on behalf of Adrian Graham <witchy at binarydinosaurs.co.uk>
Sent: Friday, February 3, 2017 2:34:18 PM
To: General Discussion: On-Topic and Off-Topic Posts
Subject: Re: Logic Analysers

On 03/02/2017 19:43, "Tony Duell" <ard.p850ug1 at gmail.com> wrote:

> But that's why I said 'about'. I am doing order-of-magnitude calculations,
> not trying to design a delay line. I would estimate that between adjacent
> ICs on the same board you'd get a delay measured in 10's or 100's of
> picoseconds. That sort of order. So a 25MHz logic analyser, with an
> effective time resolution of 40ns (if that) is not going to show it.
> There is no way you're going to get delays of 40ns between adjacent
> ICs on any reasonable PCB.

This is the sort of thing I mean:


Watching the A1 address line (no triggers just sampling 6 points) and a
pulse appears at ROM4 on the falling edge of the ALE signal but not the
other 3 ROMs or the LS373 flip-flop that's demultiplexing the AD1 pin of the
8085. While I was thinking about the possibility of propagation delay I
noticed this one:


Pulse missing from ROM3.

Given the paths on this board aren't massive and resistance is equal between
all points when measured with a DMM (and all sockets have been replaced,
traces checked etc) what else could I be looking at?

Binary Dinosaurs creator/curator
Www.binarydinosaurs.co.uk - the UK's biggest private home computer

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