HP 16550A User Reference page 98

The Trigger Menu
Assigning Resource Term Names and Values
Clear ( =X) Sets the Term Assignment fields as follows:
In Terms a-
j,
the assignment field is set to all Xs (don't cares).
In Range 1, 2 terms, the two assignment fields are set to maximum (Fs) and
minimum (Os) settings.
In Timers 1, 2 terms, the assignment field is reset to a minimum time
of 400 ns.
In Edge 1, 2 terms, the assignment field is reset to a period (.).
Set ( =1) Sets the Term Assignment fields as follows:
In Terms a -
j,
the assignment field is set to all ls (high).
This option is not available for the two Ranges Timer, and Edge terms.
Reset ( =0) Sets the assignment fields as follows:
In Terms a -
j,
the assignment field is set to all Os (low).
This option is not available for the two Range, Timer, and Edge terms.
Bit by Bit Assignment
Bit Pattern Terms Just to the right of the bit pattern name fields are
the term assignment fields. When any of the individual assignment fields
are selected, a keypad appears. Use this keypad to assign real values or
Don't Care (x) values.
Keypad
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