HP E1563A, User Manual, Page: 29 / 166

Digitizer Application Information 29
Triggering the Digitizer
Two Common
Trigger Sources per
Channel
Triggering digitizer readings across all input channels is accomplished with
one or both of the two available trigger sources (TRIGger:SOURce1 and
TRIGger:SOURce2). The trigger event can be different for each source e.g.,
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
TRIG:SOURce<n> INT<channel> command. For
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;
TRIG:SOUR INT2. Figure 2-1 illustrates the relationship of the trigger level
to the internal trigger source.
Internal Trigger Level
Detection
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
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.