Oscilloscope Question - Page 1
Forum section: electronics / beginners

author: Brentd27
author_rank: Newbie
timestamp: September 19, 2019, 06:40:40 pm
content: 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?

author: ataradov
author_rank: Super Contributor
timestamp: September 19, 2019, 06:50:53 pm
content: What do you mean by "zoomed in"? What is the actual time/div setting?Attach some screen captures.

author: Brentd27
author_rank: Newbie
timestamp: October 07, 2019, 10:30:46 pm
content: 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.

author: ataradov
author_rank: Super Contributor
timestamp: October 07, 2019, 10:46:40 pm
content: 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.

author: Ian.M
author_rank: Super Contributor
timestamp: October 07, 2019, 11:24:38 pm
content: 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).

author: james_s
author_rank: Super Contributor
timestamp: October 08, 2019, 01:15:13 am
content: Set the scope just to trigger on the edge of the reset pulse, see if it's ever happening at all. If the CPU is not working it's not entirely unlikely that the reset line is stuck active for one reason or another. Once you find the reset pulse, you can start trying to find the time relationship between that and the +5V coming up.

author: alsetalokin4017
author_rank: Super Contributor
timestamp: October 09, 2019, 08:12:19 pm
content: QuotePut a 4 or 8 GB capacity USB stick in the port at lower left next to the on-off switch. Larger drives may work too, or not. Wait a moment for the scope to recognize the stick. Then press the green button with the "Printer" symbol on it, just below the green "Help" button, at the upper right of the front panel. The scope will save the screenshot to the USB drive as a .png image file and give it a sequence number. Unfortunately since the scope does not have a realtime clock, the file save date/time will not be correct. Because of this it may help you to make a note of the sequence number and what the screen is showing, for your records. Or shift the file to your computer and rename it appropriately.Saving a screen takes a variable length of time. Sometimes it will be very quick and other times it takes a while. More complex setups may save more quickly if you stop the scope with the Run/Stop button before making the screenshot.The scope certainly does have the resolution to show a 50 ms delay between two signals on different channels! If, that is, it is set up properly and the probing is done properly. So if possible please provide a schematic or block diagram with probe points, and a screenshot or two of what you are getting on the scope.

author: JustMeHere
author_rank: Frequent Contributor
timestamp: October 10, 2019, 01:46:16 am
content: You can also use the Rigol Ultra sigma on your computer to capture traces.

author: The Senate
author_rank: Newbie
timestamp: October 11, 2019, 04:42:22 pm
content: Quote from: Brentd27 on October 07, 2019, 10:30:46 pmYou can always do the quick and dirty phone picture

author: Fungus
author_rank: Super Contributor
timestamp: October 11, 2019, 05:36:06 pm
content: Quote from: JustMeHere on October 10, 2019, 01:46:16 amYes, but that would be a bad idea. It's one of the most bloated and horrible pieces of software ever created.

author: thedoc298
author_rank: Contributor
timestamp: October 11, 2019, 10:52:43 pm
content: Quote from: Brentd27 on September 19, 2019, 06:40:40 pmHow will you see any difference if channel one is on the +5 rail already high...?

author: james_s
author_rank: Super Contributor
timestamp: October 11, 2019, 11:26:45 pm
content: Who said it's already high? I can only assume he's shutting the thing off, connecting it, then turning it on, so the scope will then trigger when the 5V rail comes up.