ADD mode adding logic signals test

Thread Starter

watsongrey

Joined Oct 31, 2014
94
I got this test from a Tektronix 2467 manual on page#70
http://exodus.poly.edu/~kurt/manuals/manuals/Tektronix/TEK 2467B Operator.pdf

It uses the ADD mode on the Oscilloscope for adding logic signals

I don't know how to use it or when would I use this type of technique, do you guys get it and know how to use it and when to use it?

Coincidence of Digital Signals
High-High Combination
Low-Low Combination
The ADD waveform is high when both signals are High
The ADD waveform is Low when both signals are Low


1.) Logic signals applied to Ch1 and Ch2
( If one logic signal is high and the other is low , invert ch2 )
2.) Set Oscope to ADD mode
3.) Set Both input coupling to DC

Now you can observe and Measure Coincidence durations
Ch3 and Ch4 can show relationships to other signals
 

Thread Starter

watsongrey

Joined Oct 31, 2014
94
I don't know how to use it or when would I use this type of technique, do you guys get it and know how to use it and when to use it?
 

alfacliff

Joined Dec 13, 2013
2,458
the add mode adds the voltages from two inputs. two high inputs would make a higher voltage. it is used to make signals more readable, from two zeros zero volts, a one and a zero, a voltage repersenting high, and two ones, giving a voltage twice as high as a normal high.
 

MrChips

Joined Oct 2, 2009
24,997
ADD mode does the opposite of SUBTRACT mode.
On older analog oscilloscopes, if you needed to subtract CHAN2 from CHAN1 you had to invoke both ADD and CHAN2 INVERT.
 

Thread Starter

watsongrey

Joined Oct 31, 2014
94
Yes i know but look how they are using the ADD mode in this technique

Now you can observe and Measure Coincidence durations
Ch3 and Ch4 can show relationships to other signals


What do they mean by Coincidence durations?
What relationships of other logic signals on Ch3 and ch4 , what kind or type of relationship?

Coincidence of Digital Signals
High-High Combination
Low-Low Combination
The ADD waveform is high when both signals are High
The ADD waveform is Low when both signals are Low


They are using the ADD mode to do this coincidence duration measurement meaning i think for a High-high combination or a low-low combination. This means that they are probing 2 inputs to a gate or 2 outputs to a gate and the ADD mode will tell if the 2 inputs are a high-high combination and if it is the ADDED waveform will be HIGH.

The way they are using the ADD mode is to get a Combination and a ADDED waveform to tell you about the combination. My question is when would you use this technique when troubleshooting logic circuits and can you please think of any examples of using this coincidence measurement?
 

Thread Starter

watsongrey

Joined Oct 31, 2014
94
the add mode adds the voltages from two inputs. two high inputs would make a higher voltage. it is used to make signals more readable

When would you use this technique to make the signals more readable? yes it will be more readable but you're summing two different input waveforms together, I can understand if you summed the two of the same inputs together which i would have to jumper or bridge the Oscope channels to input the same waveform into both ch1 and ch2. This would be useful when measuring microvolts or millivolts or measuring noises immunity in a circuit

Or how do you use this add more to make signals more readable?
 

alfacliff

Joined Dec 13, 2013
2,458
the add mode adds the voltages from two inputs. two high inputs would make a higher voltage. it is used to make signals more readable

When would you use this technique to make the signals more readable? yes it will be more readable but you're summing two different input waveforms together, I can understand if you summed the two of the same inputs together which i would have to jumper or bridge the Oscope channels to input the same waveform into both ch1 and ch2. This would be useful when measuring microvolts or millivolts or measuring noises immunity in a circuit

Or how do you use this add more to make signals more readable?
by making a larger deflection when the signals are timed the same. if BOTH are high, its twice as large a deflection as either . a kind of two stair step, one high first step both high, second step.
 

Thread Starter

watsongrey

Joined Oct 31, 2014
94
by making a larger deflection when the signals are timed the same. if BOTH are high, its twice as large a deflection as either . a kind of two stair step, one high first step both high, second step.

So it's ment for adding stairstep waveforms together to see a larger deflection of the each step?
 

BillB3857

Joined Feb 28, 2009
2,552
I sometimes use it to check for exactly equal transition times. If the signals do not transition at the same time, a notch will be seen half way up on the slope of the displayed waveform. If those same two signals were sent to the inputs of an exclusive or gate, the output of that gate would be a pulse equal to the difference between the transition time.
 

Thread Starter

watsongrey

Joined Oct 31, 2014
94
I sometimes use it to check for exactly equal transition times. If the signals do not transition at the same time, a notch will be seen half way up on the slope of the displayed waveform.

You will see a "notch" on the ADDED summed waveform?

If those same two signals were sent to the inputs of an exclusive or gate, the output of that gate would be a pulse equal to the difference between the transition time.

The Added summed waveform would be the difference between the transition time of 2 input signals?

no, it is not just for adding stairstep voltages, it adds whatever voltage is on channel 1 to whatever voltage is on 2.

Yes i know, but did u read the tektronix 2467 manual on how they did the " logic coincidence duration measurement"

It doesn't make sense to me how they are using this and is it for logic inputs or logic outputs when doing a logic coincidence duration measurement

The Logic coincidence duration measurement is looking for High-High Combinations or Low-Low Combinations , you use the ADD mode to get you these combinations
 

BillB3857

Joined Feb 28, 2009
2,552
Pictures are worth a lot. Top picture is of the two channels in CHOP mode. Lower picture is in ADD mode. Look carefully near the center of the trace. In CHOP mode, can you see any difference in transition time? Now look at the lower picture and the line going down where both signals are transitioning from high to low. See the small notch about half way down?
 

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Thread Starter

watsongrey

Joined Oct 31, 2014
94
Top picture is of the two channels in CHOP mode.

Why did u use the CHOP mode instead of display both ch1 & ch2 at the same time?
I'm not sure when or what use the CHOP or ALT modes are and when to use them

See the small notch about half way down?

Yes I see the notch, that notch is becauses its ADDED summed two different edges

You have two different pulse widths that are summed/added together

I'm not sure why the notch didn't show up in the CHOP or ALT modes but only in the added summed mode
 

BillB3857

Joined Feb 28, 2009
2,552
CHOP and ALTERNATE are the two ways that dual traces are presented on the screen. ALTERNATE does exactly what it says. One trace is made, then the other. They take turns for one full sweep time each. CHOP, on the other hand, causes very small sections of each trace to be displayed alternately. Think of it as time sharing the display at a high rate. The frequency of the built in chopper will be typically be much higher than the sweep frequency. That will allow lower frequency waveforms to appear to be displayed together, rather than one at a time.

The notch shows up because it is difficult for the eye to see such a small difference in the vertical alignment of the edges when in CHOP or Alternate.

Do you have a scope or are you just reading a manual?
 

Thread Starter

watsongrey

Joined Oct 31, 2014
94
The notch shows up because it is difficult for the eye to see such a small difference in the vertical alignment of the edges when in CHOP or Alternate.

I said the leading or falling edges are at different voltages , that is why you see a notch
but yes the vertical alignment of the edges

Do you have a scope or are you just reading a manual?

Both

CHOP and ALTERNATE are the two ways that dual traces are presented on the screen. ALTERNATE does exactly what it says. One trace is made, then the other. They take turns for one full sweep time each. CHOP, on the other hand, causes very small sections of each trace to be displayed alternately. Think of it as time sharing the display at a high rate. The frequency of the built in chopper will be typically be much higher than the sweep frequency. That will allow lower frequency waveforms to appear to be displayed together, rather than one at a time.

When I use Alternate mode, it causes flickering and alternating back and forth between Ch1 waveform and Ch2 waveform

The CHOP mode, will chop the positive and negative cycles into small sections

I'm not sure when would I use the CHOP mode
 

BillB3857

Joined Feb 28, 2009
2,552
Since you have a scope, turn the time base down to .5sec/div and enable both traces. Set mode to ALT and watch the traces. One, then the other will display. Now, leave the time base at the same .5sec/div and change the mode to CHOP. What is the difference in the display. How easily could you compare timing in the ALT mode vs the CHOP mode?
 

Thread Starter

watsongrey

Joined Oct 31, 2014
94
How easily could you compare timing in the ALT mode vs the CHOP mode?

In the Alt mode it is better to compare timing
When do you use the ALT mode and CHOP mode? for what type of circuits, waveforms or frequency?
You're using the CHOP mode to compare timings, but for what kind for waveforms and at what frequency

When I use a Oscope i just turn on both traces and set it to vertical mode
I don't use the ALT mode or CHOP mode because i don't know what they are used for or how to use them for what kind of waveforms, circuit tests, and at what frequency
 

BillB3857

Joined Feb 28, 2009
2,552
Did you turn the trace down to a slow speed before trying the ALT vs CHOP? What control are you setting to vertical mode? A scope is a very important tool for electronics but to define what would you use it for is difficult until you need it. When you need it to display a certain signal in a certain way, you will need an understanding of what each control does and why it does it.
 
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