depends on the signal you're looking at. e.g. looking at an active low enable that causes a design to crash and burn as soon as the enable is applied You probably want to check the falling edge of the enable in relation to other signals.When measuring waveforms or signals , when do you use or want to use the Negative or Positive trigger on the Oscope?
No, depends on what you are trying to look at. For a repetitive signal like a clock positive or negative triggering looks pretty much the same. Instead think of what happens if you are looking at a non-repetitive pulse of 1 ms and you need to look at another signal that has serial data on it that starts 100 ns after the rising edge of the pulse but end 1 us later. If you are triggering on the falling edge unless you have a DSO with with a huge buffer you won't have any resolution to look at the the leading edge of the pulse and the serial data.stanleystan said:If you have are measuring logic TTL or Cmos waveform/signals, using the negative or positive trigger will give you the same result?
Yes and yesstanleystan said:The Negative Triggering is used when you want to measure a negative transition or when a voltage is switching from a positive voltage to a negative state
The Positive triggering is used when you want to measure a positive transition or when a negative voltage is switching to a positive state
I've already given a few cases.stanleystan said:Is there any other examples to use the negative triggering to do other kinds of measurements?
When would you want to use the negative triggering? for what kind of measurements?
Look at the signal and what you are trying to capture. If the signal(s) of interest occurs around the falling edge of the triggering event use a negative edge trigger. If the signal(s) of interest occur around the rising edge of the triggering event use a positive edge trigger.stanleystan said:How do you know which triggering polarity to use to do what kind of measurements? how do you know which polarity to choose?
Not sure what you mean by this. You normally adjust the waveform to some V/div setting and set the trigger to somewhere around the logic levels trigger level. If you were looking at undershoot problems you would likely set the trigger to less than 0V and the V/div to something really small like 10mV/div. Depends on what you are trying to look at.stanleystan said:When Magnifying a small waveform , the triggering level and triggering polarity has to be fine adjusted?
How about looking at the ramp up and ramp down of a power supply. You certainly don't use a rising edge trigger to monitor the voltage supply ramp down, unless you are trying to trigger on a non-monotonically decreasing supply rail to look at the problem.I do need more examples of when you would want to use positive or negative triggering and which polarity to choose
What are you looking at, clocks, sine/cosine waveforms? Anythng periodic isn't very interesting on a scope.stanleystan said:Mostly when I choose the polarity of the triggering it seems to give the same result, why is that? when does the result change when choosing the polarity of the triggering?
If you can't figure this out you're in for a world of hurt when you need to debug a board with a scope. I've already give some scenarios of why you would use different triggering.stanleystan said:What logic signals do you use the negative triggering when do what kind of measurements?
Not true you may want to look at the active edge of the active low signal or the inactive edge of the active low signal. Depends on what else you are looking at on the OTHER scope probe(s).stanleystan said:I know if the IC Logic chip is Negative triggered or needs a negative input , you use the negative triggering on the Oscope
Because you're probably looking at only one signal and it's probably a clock or some other non random periodic signal.stanleystan said:But I'm not sure when to use the negative or positive triggering for signals, because they mostly give me the same result, so I'm confused when it changes the result or out come
You probably want to check the falling edge of the enable in relation to other signals.
What are you looking at, clocks, sine/cosine waveforms? Anythng periodic isn't very interesting on a scope.
Not true you may want to look at the active edge of the active low signal or the inactive edge of the active low signal. Depends on what else you are looking at on the OTHER scope probe(s).
This isn't what I mean. I'm saying using various trigger polarities allows you to look at other signals on different scope probes (other than the one you are using as the trigger) in relation to the triggering scope probe. Say the trigger is on the scope probe with the clock showing and a data bit is on a second scope probe and you want to see if the data arriving at the pins of a device can be captured by the device input register. If you turn on persistence in the scope you'll get a screen full of all the transitions in relation to the triggering edge of the clock. If the capture of data is on the falling edge in the device it makes no sense to use a rising edge trigger as you wouldn't be synchronizing to the falling edge, which is what the device is looking at to capture data.So the Triggering Polarity only works when it's compared or in "RELATION" to other signals?
The Triggering Polarity only works when you use the External trigger input on the Oscope?
If you don't compared other signals or use the External trigger input on the Oscope, the triggering polarity of the oscope won't give you a different result?
I don't think you've actually looked at the signal when you change the trigger polarity and absolutely nothing else on the scope's settings. Do this and observe carefully. You will witness the signal moving left/right by half a clock cycle. That is the difference. You need to look at signals that are NOT clocks, then you might have a better understanding. Look at the output of a PWM or something else that isn't a clock.stanleystan said:Yes Clocks signals, TTL or CMOS logic signals that are Periodic
So the Trigger Polarity will give the same result to periodic signals?
The Trigger Polarity will only change the result with Non-Periodic signals?
Active edge and the Inactive edge will give you the same result , what is the difference?
You will witness the signal moving left/right by half a clock cycle. That is the difference.
There are several reasons for wanting the o-scope display to start at a specific polarity. One is that you may be interested in measuring the rise time or fall time of a signal. Often the thing that affects the rise time is not the same thing that affects the fall time, so being able to look at one edge or the other is crutial.Yes it does moves left/right by some microseconds or time
But the Pulse width and Time Period of the waveform stays the same, in either triggered polarity
So I still don't get what the triggered polarity does, when it doesn't change the pulse width or time period of the waveform you're looking at
It only shifts left to right when you're viewing multiple Logic TTL or CMOS signals on multiple channels
But why would you care to know if the Logic signal is triggered to a Positive or negative? it's just a different reference or starting point..
One is that you may be interested in measuring the rise time or fall time of a signal.
Another reason is that you may want to measure the delay between one signal and another signal. The delay starting at the positive edge may be very different from the delay starting from the negative edge, so again you would want to be able to control which edge is synchronized with the beginning of the o-scope display.
Since this output is inverted, the resting state is logic high (say, +5v)
No. Don't try to extract an "always" from an example. Each application is different. When you know what you want to measure, then you will know which polarity to use. Many times it doesn't make any difference. But sometimes it does. Only experience and knowledge of the application will tell you when that is.So you use always the negative polarity trigger when you're measuring Inverted Logic or Inverted signals?
Many times it doesn't make any difference.
Of course. Many times I am just interested in measuring the period of a strictly periodic waveform. Then I don't even bother looking to see if my scope is set for positive or negative triggering because I will get my answer more quickly by just looking at the waveform regardless of how it is triggered. But I also gave you one example of when it does matter. So it is good to know how to do it when you need to.So you have noticed that too, because I don't get a difference mostly , it gives me the same result with either positive or negative polarity..
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