Triggering on Waveforms
3–74 TDS 684A, TDS 744A, & TDS 784A User Manual
If you choose Accept Glitch, the oscilloscope will trigger only on pulses
narrower than the width you specified. If you select Reject Glitch, it will trigger
only on pulses wider than the specified width.
Set the Level. To set the trigger level with the Level main menu (or the front
panel trigger LEVEL knob), press TRIGGER MENU ➞ Type (main) ➞ Pulse
(pop-up) ➞ Level (main) ➞ Level, Set to TTL, Set to ECL, or Set to 50%
(side).
If you select Level, you set the trigger level by entering a value with the
general purpose knob or the keypad.
If you select Set to TTL, the oscilloscope sets the trigger level to the TTL
switching threshold.
If you select Set to ECL, the oscilloscope sets the trigger level to the ECL
switching threshold.
If you select Set to 50%, the oscilloscope searches for the point halfway
between the peaks of the trigger source signal and sets the trigger level to
that point.
To Set Mode and Holdoff. Mode and holdoff can be set for all standard trigger
types and classes. To set mode and holdoff, refer to To Set Mode & Holdoff on
page 3–59. To learn more about trigger mode and holdoff, see the descriptions
Trigger Modes and Trigger Holdoff on page 3–51.
When you select the pulse class Runt, the oscilloscope will trigger on a short
pulse that crosses one threshold but fails to cross a second threshold before
recrossing the first. To set up for runt triggering, do the following procedures.
Select Runt Triggering. Press TRIGGER MENU ➞ Type (main) ➞ Pulse
(pop-up) ➞ Class (main) ➞ Runt (pop-up). (See Figure 3–45.)
Select the Source. To specify which channel becomes the pulse trigger source:
Press TRIGGER MENU ➞ Type (main) ➞ Pulse (pop-up) ➞
Source (main) ➞ Ch1, Ch2, Ch3, or Ch4 (side). The source selected becomes
the trigger source for all four trigger classes.
Select the Polarity. To specify the direction of the runt pulse:
Press TRIGGER MENU ➞ Type (main) ➞ Pulse (pop-up) ➞ Class (main) ➞
Runt (pop-up) ➞ Polarity (main) ➞ Positive, Negative, or Either (side).
Positive looks for positive-going runt pulses.
To Trigger on a Runt Pulse