Keithley 2750 User Manual page 212

Model 2750 Multimeter/Switch System User's Manual Scanning 7-7
STEP operation overview — When the STEP key is pressed, the Model 2750 leaves the
idle state, closes the first channel, and waits for the programmed trigger event. After the
trigger is detected, the instrument may be subjected to one or more delays before perform-
ing the measurement.
After a reading is taken and stored in the buffer, the Model 2750 outputs a trigger pulse,
opens the closed channel, and then closes the next channel in the scan list. The instrument
then waits for another trigger event to measure the channel. After the last channel is
scanned, the instrument returns to the idle state with the first channel in the scan list
closed.
SCAN operation overview — When the SCAN key is pressed, the Model 2750 leaves the
idle state, closes the first channel and waits for the programmed trigger event. After the
trigger is detected, the instrument may be subjected to one or more delays before perform-
ing the measurement.
After a reading is taken and stored in the buffer, the Model 2750 opens the closed channel,
and then closes the next channel in the scan list. Operation keeps looping around to mea-
sure all channels in the scan list. After the last channel in the scan list is measured, the
Model 2750 outputs a trigger pulse.
If programmed to again scan the channels in the scan list, the Model 2750 will wait at the
control source for another trigger event. After all the scan list channels are again mea-
sured, the Model 2750 will output another trigger pulse. After all programmed scans are
completed, the instrument returns to the idle state with the first channel in the scan list
closed.
The individual components of the trigger models are explained as follows:
Idle
When a scan is enabled (STEP or SCAN annunciator on), operation goes into the idle state
and immediately drops down to the control source. Note that after the last channel in the
scan is measured, operation returns to the idle state, where measurements are halted and
the first channel in the list is closed.
Control sources
For front panel operation, there are three control sources to manage the scan: Immediate,
Timer, and External Trigger. Operation is held up at the selected control source until the
appropriate trigger event is detected.
STEP operation — When the trigger event is detected, a channel is measured. The scan
pointer then loops back to the control source and waits for the next trigger event to occur.
SCAN operation — When the trigger event is detected, all the channels in the scan list are
scanned. The scan pointer then returns to the control source and waits for the next trigger
event to be detected.