HP 8901B

Operation Model 8901B
TRIGGER MODES (TO and T1)
Free Run Mode (TO).
This trigger mode is in effect in local operation, and is also in effect in remote
when Trigger Hold mode has not been selected. Measurements are made and measurement data updated
as rapidly
as settings can be changed without regard for settling of ANY internal or external circuitry
or setting changes.
NOTE
The Modulation Analyzer is always in nee-run trigger mode (TO) after
receiving a Device Clear (DCL) message, entering remote from local,
or receiving Instrument Preset (IP).
Measurements might NOT be completed if nee-run (TO) is used if
there is HP-IB activily between other HP-IB devices (e.g. a controller
talking to another instrument) during the measurement. Digger
Immediate (T2)
or Digger with Settling (T3) should be used under
these conditions.
Trigger Hold Mode (Tl).
In Trigger Hold mode, internal settings can be changed by the instrument
itself
or by the user via the bus; however, the instrument is inhibited from outputting any data to the
front-panel key lights and display,
or to the HP-IB until it receives a trigger. The following data can
be sent before the trigger
is received
A Service Request message if an enabled LIMIT is reached, or if an HP-IB code error occurs.
The Status Byte if the instrument is serial polled. (A serial poll, however, will trigger a new
measurement, update displays and return the instrument to Trigger Hold.)
Measurement data is replaced with data acquired from subsequent triggered measurement cycles.
NOTE
When a trigger is received, the Modulation Analyzer will not allow its
measurement cycle to be interrupted. (Indeed, handshake of bus commands
is inhibited until the measurement cycle is complete.)
Entering Trigger Hold. The instrument is placed in this mode after it receives the programming
code
T1 or after a triggered measurement has been executed. This mode can then be used to set
up the instrument for new measurements which are executed by a trigger.
Triggering Measurements from Trigger Hold. When a measurement is triggered from
Trigger Hold mode, the instrument makes the measurement. The display is updated
as the new
measurement cycle begins. The Status
Byte will be updated (and the Service Request message
issued
if required) by the events that occur during the new measurement cycle.
Any of the following events will trigger a new measurement cycle when the instrument is in
Trigger Hold
a. instrument receives a trigger,
b. instrument receives its listen address,
c. instrument receives GTL (Go To Local),
After the measurement is made, the instrument waits for the measurement results to be read.
While waiting, the instrument can process most bus commands without losing the measurement
results. Once the
data (measurement results) are read onto the bus, the Modulation Analyzer
returns to the Trigger Hold mode.
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