Strange delays (Analyzer 24MHz, 8ch + Logic 2 v2.3.55)

1

Hi,

I want to make an arduino pro mini 16MHz based “emulator”, which requires responses within 15usec from the trigger. I had several measurements and I was really mad about it. Anything I tried I got ~11.5usec delay from the trigger to the first command in the top prio interrupt. Then I disabled all interrupts and I made the rising edge detection and the response form the main program. The same. I had disassembled the code. Everthing was OK, nothing justified the ~11.5usec delay. Simply there was nothing between the “while” and the first command of the response.

I use a Saleae Logic Analyzer 24MHz-8ch with Logic 2 v2.3.55.

Now I tried to change the input and output pin on arduino. Then start Logic 2, triggering rising edge of input pin. Now ~8usec delay.

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Some hint: the during the while cycle in which I wait for the rising edge I create a square wave (125ns On, 375ns OFF). After getting the rising edge double on and double off (250ns, 250ns) and 3 time on-off (125ns, 125ns)

During this measurement ch1 was the input and ch2 the output, trigger was ch1 rising.

Then I switched the measuring channels and the trigger.

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As you can see, now everything is prefect. After rising edge of input, the on-off cycle ran, exited the while cycle, double on, double off, 3x on-off.

Counter-test again. Input ch1, output ch2, trigger ch1 rising. The same delay again.

I made a “counter counter-test”, I switched the measuring wires. The wires are perfect. The delay occurs when input and trigger is on ch1.

Can someone explain it?

Is it Saleae Analyzer fault or Logic 2 v2.3.55 bug? (I barely think that the arduino can do such strange things as it looked like the edge detection delayed 11,5usec)

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@mernok1 This is definitely strange. I can’t say I know what’s going on here unfortunately. How exactly are you changing the input and output pin on the Arduino? Are you doing it in code without swapping the Logic wires? Or are you swapping the Logic wires without changing the code?

  • If you are changing the code, the delay is likely caused by the Arduino
  • If you are physically swapping the wires and not changing your code, then it does seem to point to some kind of input impedance variation in your Logic (still doesn’t quite make sense how that would case a digital response delay though, but it seems to be the most prime suspect). It’s hard to believe it would be coincidence if you kept swapping the wires back and forth and noticed a consistency in delay timings.

Also, which exact Saleae Logic model do you own? You can refer to the photos below. We have a few 8 channel devices and I’d like to know your exact model number:

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hi,

sorry for the late answer. I only swapped physically the wires, every other thing remained the same.

And what a shame. :man_facepalming: Based on your identification guide I discovered that my product (it was a gift…) is a chinese copy. (looks like this: Saleae Logic Analyzer Knockoff Hacking | Hackaday )

I am really sorry for disturbing you with chinese crap. :zipper_mouth_face:

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@mernok1 Ah I see - that might explain it. Apologies we’re unable to help debug that for you.