Logic Analysers

Adrian Graham witchy at binarydinosaurs.co.uk
Fri Feb 3 12:47:55 CST 2017

On 03/02/2017 16:41, "Jon Elson" <elson at pico-systems.com> wrote:

> 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.

Neither of them can go that fast but I didn't think that was necessary since
the system clock on this machine is 6MHz so sampling at 25+ should be
sufficient. If I reduce the number of channels to 6 I can drive one of them
at 50MHz but that didn't seem to make a difference.

> 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.

So am I :) I mean, the most expensive one was ukp40 direct from China so if
it's not fully accurate I can't really be surprised. I have a Zeroplus
coming next week from another collector who used it on Apple][/PETs as well
as car ECUs with good results. In the meanwhile the external clock signal
from the 8085 on this machine is accessible in 3 locations so I'll try 3
channels and see if it's properly square.
> (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.)

I'm looking at a lower-end HP/Agilent for around ukp200-250 which should be
enough since I doubt I'll ever work on anything with a clock speed of more
than 8MHz.

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

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