Semi-Synchronous Operation - Keithley 7001 Instruction Manual

4.11.2 Semi-synchronous operation

In the Semi-Synchronous Trigger Link mode all trig-
gering (input and output) in the test system is con-
trolled by a single line. When the normally high (+5V)
trigger line is pulled low (0V), a trigger occurs on the
negative-going edge. When the trigger line is released,
a trigger occurs on the positive-going edge (see Figure
4-26). The advantage of this single line trigger is that as
long as one of the instruments in the system holds the
line low, the trigger is suppressed. In other words, the
trigger will not occur until all instruments in the sys-
tem are ready.
Trigger on
negative-going
edge
≈ +5V
0V
Pulled low by
first instrument
Figure 4-26
Semi-synchronous trigger link pulse specifications
IN
OUT
Trigger
Link
Meter
Figure 4-27
Typical semi-synchronous mode connections
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Trigger on
positive-going
edge
Released by
second instrument
Trigger Link
Cables (2)
(8501)
Line #1
7001 Switch System
For example, assume that a meter (equipped with Trig-
ger Link) is connected to two Model 7001s for semi-
synchronous operation as shown in Figure 4-27. All
three instruments are programmed to use trigger line
#1. The two Model 7001s have relay settling times of
10msec and 50msec respectively.
Assume that the meter initially performs a measure-
ment. After the reading is done, the meter will drive
the trigger line low. The negative-going edge will trig-
ger both Model 7001s to close a channel. While the
Model 7001s are in the process of closing a channel,
they will hold the trigger line low. Ten milliseconds af-
ter switch closure, the first Model 7001 will release the
trigger line. However, the second Model 7001 will con-
tinue to hold the line low since it is not finished. Fifty
milliseconds after switch closure, the second Model
7001 will release the trigger line. The positive-going
edge will trigger the meter to perform a measurement
and subsequently pull the trigger line back down to
close the next channels. This process continues until all
channels are scanned and measured.
IN
OUT
Line #1
Trigger
Link
Front Panel Operation
IN
OUT
Trigger
Link
7001 Switch System
4-59