Electronics > Beginners
Oscilloscope Question
Brentd27:
This is a bit of an "Am I doing this right?" question.
I have a Rigol DS1054 oscilloscope (with the 100Mhz firmware). I'm working on an arcade MPU that uses an MC6800 CPU. I'm wanting to test the reset delay between power on and when the reset line goes high.
I tried setting the scope to single shot, connecting channel one to the +5V power rail, and channel 2 to the reset line, then setting the trigger to activate when the channel 1 starts to go high. I get a capture, but it doesn't seem to show any delay between the two pulses, even zoomed in.
Is the delay beyond the resolution of my scope, or am I doing this wrong?
ataradov:
What do you mean by "zoomed in"? What is the actual time/div setting?
Attach some screen captures.
Brentd27:
Sorry for the delay in getting back. Not sure how to do screenshots on the Rigol yet.
I've tried several time/div settings from 20ms to 100ms. The delay between power on and reset signal is supposed to be ~50ms.
When I said "zoomed in", I was referring to increasing the horizontal scale on a single-even trace. (i.e. making each division show smaller time increment).
I've checked my trigger levels to make sure they're sane. (Trigger set at about ~2.4V for a 5V signal)
The scope is still showing both signals immediately going high as soon as the power comes on, with no delay.
ataradov:
Can you show the circuit that is supposed to generate that 50 ms delay? It is really hard to tell something meaningful without any information.
Ian.M:
That certainly sounds like your reset delay circuit isn't working.
To prove it isn't something wrong with your scope settings, hook up a test RC circuit to the 5V rail. Use a 10K resistor to charge a 10uF cap, which gives a time constant of 100ms, so, if the power comes on sharply you should see a decaying exponential charging curve, reaching 63% of the rail voltage in approx 100ms (depending on ramp-up rate of the rail and component tolerances).
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