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ARM
The ARM command subsystem controls the third state in a four state measurement
process. The four states which occur during a successful reading are idle, initiated,
wait-for-arm, and wait-for-trigger. The last two states have event detection
associated with them which control when they exit the current state. These four
states are more fully described as follows:
• Idle -- In this state, the instrument is not sampling. This is the state where setting
changes are done via commands to the instrument. This state is exited when an
INITiate command is received. This state is returned to after a reset, after
successful completion of measurement, or after a measurement is aborted.
• Initiated -- Once the instrument is initiated with the INITiate command, it passes
through this state, and continues down to the wait-for-arm state if all readings are
post-arm and ARM:COUNt is not yet satisfied. If pre-arm readings are specified,
the digitizer passes through to the wait-for-trigger state.
• Wait-for-arm -- In this state, the instrument waits for the specified ARM event to
occur before progressing to the wait-for-trigger state to make a measurement.
• Wait-for-trigger -- In this state, the instrument waits for the specified trigger event
to occur, and when it occurs, a reading is taken. After a reading is taken, the
cumulative number of readings taken is compared to the count specified in
TRIGger:COUNt or SENSe:SWEep:POINts. When the count is reached, the state
is exited, otherwise, the instrument waits for another trigger and takes another
reading. Upon exit from this state, the instrument returns to the initiated state and
checks to see whether or not ARM:COUNt is satisfied. If the arm count is
reached, the instrument returns to the idle state. If not, another loop is executed by
entering the wait-for-arm state.
The following controls can be specified from the ARM subsystem:
• The event(s) which will cause the transition out of the wait-for-arm state
(ARM:SOURce1 and ARM:SOURce2). There is a rich set of event sources to
choose from, and when both sources are enabled (neither set to source HOLD), a
logical OR of the two sources occurs. The occurrance of the appropriate event on
either source will cause the HP E1429 to exit from the wait-for-arm state.
• The number of start arm events to occur before the digitizer returns to the idle
state (ARM:COUNt). Another way to think of this is the number of bursts of
readings which will occur.
186 Command Reference ARM Subsystem