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Logic Triggering
TDS 620A, 640A & 644A User Manual
3Ć79
Mode & Holdoff
You can change the holdoff time and select the trigger mode using this
menu item.
1. Press TRIGGER MENU ➞ Type (main) ➞ Logic (popĆup) ➞
Class (main) ➞ Pattern or State (popĆup) ➞ Mode & Holdoff (main) ➞
Auto or Normal (side).
H In Auto mode the oscilloscope acquires a waveform after a specific
time has elapsed even if a trigger does not occur. The amount of
time the oscilloscope waits depends on the time base setting.
H In Normal mode the oscilloscope acquires a waveform only if there
is a valid trigger.
2. Press Holdoff (side). Enter the value in percent using the general purĆ
pose knob or the keypad.
Depending on whether you chose the class Pattern or State, there are
different menus for defining the channel inputs and the combinational logic.
When you select Pattern, the oscilloscope will trigger on a specified logic
combination of the four input channels. See page 3Ć77 for details on operaĆ
tions common to both pattern and state triggers.
Define Inputs
To set the logic state for each of the input channels (Ch1, Ch2, ...):
1. Press TRIGGER MENU ➞ Type (main) ➞ Logic (popĆup) ➞
Class (main) ➞ Pattern (popĆup) ➞ Define Inputs (main) ➞ Ch1, Ch2,
Ch3,orCh4 (side). (On the TDS 620A, Ch3 and Ch4 are replaced by
Ax1 and Ax2.)
2. Repeatedly press each input selected in step 1 to choose either High
(H), Low (L), or Don't Care (X) for each channel.
Define Logic
To choose the logic function you want applied to the input channels (see
page 3Ć76 for definitions of the logic functions for both pattern and state
triggers):
Press TRIGGER MENU ➞ Type (main) ➞ Logic (popĆup) ➞
Class (main) ➞ Pattern (popĆup) ➞ Define Logic (main) ➞ AND, OR,
NAND,orNOR (side).
Pattern Operations