Author Topic: HP 16500 Logic Analyzer "doesn't like" clock signal (thinks it's always high)  (Read 466 times)

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Offline PhaseseekerTopic starter

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Pretty much as the title states; HP16500 + 16510 State/Timing card, in state mode. The analyzer complained about the clock being slow or missing, so I connected it to one of the input channels (same pod) and it sees it as always high. I checked with a scope and the clock is there, there's a bit of ringing but it might be caused by the way I was probing it, either way the device that uses that clock runs without issues.
The clock signal in question is a 4MHz clock being generated from an ATTiny85 with TMR0 in CTC mode (internal oscillator set at 16MHz and divided by the timer to 4MHz); I did this because I didn't have an oscillator module of the right frequency and the device under test doesn't have the ability to output a clock when run from its internal oscillator.
 

Offline jmelson

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I use Tek analyzers.  But, can it view the clock channel as an ordinary data channel in timing mode?  That would allow the analyzer to self-clock.  Then, you could tell if the clock channel was bad, or not connected.  Does this analyzer have variable logic levels?  Check what logic voltages it is set for.
Jon
 

Offline PhaseseekerTopic starter

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I did some more testing, turns out the problem was in what HP calls "tip isolation network", basically a small RC circuit which is put in series with each channel to terminate the cable. I made my own PCBs with said RC networks and turns out I managed to swap two of the resistors on some of the lines. Obviously the last place I checked, since I had already used the PCBs without issues (on systems with slower clocks)...
Thanks anyway
 


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