Reference
Logic Triggering
There are two classes of logic triggering: pattern and state.
A

pattern

trigger occurs when the logic inputs to the logic function you select
cause the function to become TRUE (or at your option FALSE). When you
use a pattern trigger, you define:
The precondition for each logic input — logic high, low, or do not care (the
logic inputs are channels 1, 2, 3, and 4 for the TDS 640A & TDS 644A
and 1, 2, Aux 1, and Aux 2 for the TDS 620A & TDS 524A)
The Boolean logic function — select from AND, NAND, OR, and NOR
The condition for triggering — whether the trigger occurs when the Bool-
ean function becomes TRUE (logic high) or FALSE (logic low), and
whether the TRUE condition is time qualified (see page 3-83).
A

state

trigger occurs when the logic inputs to the logic function cause the
function to be TRUE (or at your option FALSE)

at the time

the clock input
changes state. When you use a state trigger, you define:
The precondition for each logic input, channels 1, 2, and 3 for the
TDS 640A & TDS 644A (1, 2, and Ax1 on the TDS 620A & TDS 524A)
The direction of the state change for the clock input, channel 4 (Aux 2 for
the TDS 620A & TDS 524A)
The Boolean logic function — select from clocked AND, NAND, OR, and
NOR
The condition for triggering — whether the trigger occurs when the Bool-
ean function becomes TRUE (logic high) or FALSE (logic low)
Table 3-4 on page 3-80 lists the preconditions required for each logic function
to issue a pattern or state logic trigger.