How to slow down or stop fasting moving signal in Analog Scope?

[naseeam]

I'm measuring Signal that is Logic LOW for 10ms and then Logic HIGH for about 80ms.
I'm using GW INSTEK Model GOS-620 Analog Scope. It is 20MHz Scope.

The signal that I'm measuring is moving really fast. I played will all timebase settings and trigger levels but I can't get the signal to slow down or stop on the screen.
The signal is generated by my software running on 68HCS12 based target board. I'm measuring one of the ouputs which is LOW for 10ms and then HIGH for about 80ms, and this keeps repeating.

If I display sine or square wave from a function generator, I can see nice wave on my scope display. It is still, not moving.

How can I prevent my digital signal from moving so fast on the screen?

Thank you!

 

[Dean Huster]

It sounds like you're still not getting the scope to trigger correctly. Most scopes have trigger settings for INTernal trigger source and AC trigger coupling. In addition, the timebase should have an AUTOmatic setting (vs. NORMal or SINGLE sweep). There's also a trigger slope control, set for either positive (+) or negative (-) and the trigger level control. The slope is normally set to positive, depending upon whether you're wanting to view the initial edge as a positive-going edge (+ slope) or a negative-going edge (- slope). The trigger level control should be set somewhere around zero level.

On the vertical amplifier section, you may have a trigger source selector also, for Channel 1 or Channel 2. Select whichever channel the waveform of interest is on. After that, if you have a viewable signal within the bandwidth limits of the scope that is at least one vertical division high, you should be able to diddle with the trigger level control and get the waveform to solidly trigger.

 

[crutschow]

Set the horizontal sweep rate to about 10ms per division. The set the trigger per Dean's instructions.

 

[naseeam]

My coupling is set to DC. My trigger is set to AUTO. There is no AUTOmatic setting in the timebase. I got my trigger set to positive. I have tried all trigger level from zero to most positive. On the vertical amplifier, my trigger selector is Channel 1.
My horizontal sweep rate is se to 10ms per division.

How do I know if my signal is within bandwidth limits of the scope? The scope is 20MHz. The signal being measured is digital signal.

This is probably not a periodic signal. Is it possible that's why I am not getting a solid trigger.

I see the signal go logic LOW for 10ms. It happens really fast.

When signal is HIGH, it's 24V. When signal is LOW, it's 0V. It's mostly HIGH. When I turn trigger level knob, I don't know what voltages are indicated by
the trigger level.

How does trigger work? After signal is swept across the screen, then tirgger level probably does match the level of the signal, therefore I don't see the solid signal.

 

[bountyhunter]

NORMAL trigger mode might work better. Adjust level to trigger on rising edge.

 

[ghostman11]

yeah you need norm triger mode auto mode will triger itself. do you have a manual for the scope?
mind you ive got so used to using my DSO i cant remember off hand how to set my analogue scope up i will have to have a play with it later

 

[unclejed613]

you also have to make sure your trigger IS in fact set to internal, and the correct trigger type (usually the selections are DC, TV, AC-LF, and AC)... TV or AC should work... trigger source (usually has EXT, EXT/10, LINE, and INT settings) set to INT. if the trigger control has a holdoff control it should be set to OFF. if the internal trigger has it's own SOURCE switch, it should be set to whichever vertical channel you are using...

 

[naseeam]

Norm trigger mode worked. Now, I get still solid signal.

Thank you all for your help.

 

[Dean Huster]

If your signal is non-perodic such as a digital data stream vs. a plain-Jane square wave, you'll probable never get it to trigger correctly. Sometimes there are circuits that have a "frame" pulse available for triggering and you can at least trigger on that and look at the following data, a fairly easy task if you have a delayed sweep scope. Still, the waveform will be gibberish unless it's somewhat perodic where characters are repeated over and over, much like sending RYRYRYRYRYRYRY in the old Baudot teletype systems which generated a square wave.

Although your AUTO/NORM switch seems to be in the triggering section, it actually is a sweep function. Take it from an old oscilloscope guy.