Logic Analysers

Jon Elson elson at pico-systems.com
Fri Feb 3 10:41:17 CST 2017

On 02/03/2017 02:55 AM, Adrian Graham wrote:
> Ah yes, sorry, I'm aware of that. What I meant in this 
> specific case is that with 4 2764s right next to each 
> other with a direct signal path between adjacent address 
> and data pins that has a resistance of 0.5 ohms pin to pin 
> surely I should be able to put a clip on each (for 
> example) A4 address line and see the same pulse at all 
> four channels? 
Well, if the two logic analyzers were synched together, or 
you were sampling at 100 MHz or above, then yes.
But, if the logic analyzers are running too slow, sampling 
irregularly (I have no trust in Chinese gizmos until PROVEN 
that they do it right) you could get very different 
results.  Is there a clock on the microprocessor that you 
can check?  Maybe something like a baud rate clock or 
something that is at a few MHz.  See if that shows up as 
totally regular square waves.  If not, then the LA may not 
be sampling at a regular rate, or might have gaps while 
sending data to the PC.  I'm just suspicious of these units, 
given the results you report.

(On my $130,000 Tektronix analyzer, I don't have to worry 
about such stupid stuff, I know they got it right.  I paid 
less than $750 for it, it will do 100 MHz on 288 
synchronized channels, with a 128K record length.  But, it 
is bigger than a big kitchen microwave, and much noisier, too.)


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