Triggering The Digitizer - HP E1563A User Manual

Triggering the Digitizer

Two Common
Triggering digitizer readings across all input channels is accomplished with
one or both of the two available trigger sources (TRIGger:SOURce1 and
Trigger Sources per
TRIGger:SOURce2). The trigger event can be different for each source e.g.,
Channel
SOURce1 can be EXT and SOURce2 can be TTLT0. You use the
TRIG:SOURce<n> command to set the trigger source event options which
can be OFF | BUS | EXT | HOLD | IMMEDIATE | INTernal1-4 | TTLT0-7.
You must execute the TRIG:SOURce<n> command two times to set both
trigger sources (TRIG:SOUR1 and TRIG:SOUR2). At power-up and after
resetting the module with *RST, TRIG:SOUR1 defaults to IMM and
TRIG:SOUR2 defaults to HOLD. The number of readings set by the
SAMPle:COUNt command are taken after the trigger event occurs.
Note
Do not confuse TRIG:SOUR1 as being associated with only channel 1 (as
well as TRIG:SOUR2 with only channel 2). Both sources are common to
ALL channels and the "1" and "2" are not channel designators but "source"
designators.
Internal Triggers
Using SCPI or Plug&Play, you can trigger internally off of a voltage level
from any channel. Trigger level is set using the
TRIG:LEVel<channel>
< voltage > command for the particular channel you want to generate the
trigger event. You then set the trigger source to trigger internally from that
channel using the command. For
TRIG:SOURce<n> INT<channel>
example, if you want to trigger from a 11.5V level on channel 2, you send
the following commands:
VOLT2:RANG 16; TRIG:LEV2 11.5;
Figure 2-1 illustrates the relationship of the trigger level
TRIG:SOUR INT2.
to the internal trigger source.
Internal Trigger Level
Each channel has a level compare circuit that compares the input signal to
the value set by the TRIG:LEVel<channel> command. This level initiates
Detection
a trigger when the input signal equals OR EXCEEDS the value set by the
TRIG:LEVel command. This means the trigger can occur at a value other
than the value set by the TRIG:LEVel command. For example, assume a
trigger level of 0V on a ramp from -1V to +1V. The first samples may be
negative values close to zero. These values will not cause a trigger because
they do not equal or exceed the trigger level value yet. The next sample may
be a positive value greater than the trigger level. The trigger compare circuit
(see Figure 2-2) detects this level is equal to or greater than the trigger level
value set and a trigger is generated. It was not however, generated at the
exact trigger level value set by the TRIG:LEVel command.
Digitizer Application Information 29