Agilent Technologies VXI E1439 - Manual (Page 33)

23
Using the Agilent E1439
The measurement loop
The measurement loop
The measurement loop progresses through four states. The transition from one state to the next is
tied to the transition of the Sync signal. The effect of the Sync signal is summarized in the
following diagram representing the four possible states of an Agilent E1439 module.
In the Idle state, the E1439 places no new data into the FIFO output buffer memory although
previously measured data is retained in the buffer memory and is available for output via the
VME (and also local bus, or fiber optic transmitter port on the E1439D). The module stays in the
Idle state until the Sync line is asserted.
Upon entering the Arm state the E1439 clears old data. It remains in the Arm state until the Sync
signal is released. If an E1439 is programmed with a pre-trigger delay, it collects enough data
samples to satisfy this pre-trigger delay, and then releases the Sync line. If no pre-trigger delay
has been programmed, the module releases the Sync line immediately. When all E1439s in a
system have released the Sync line, the module moves to the Trigger state.
Upon entering the Trigger state, an E1439 that is programmed with a pre-trigger delay continues
collecting data into the FIFO, discarding any data prior to the pre-trigger delay. An E1439
remains in the Trigger state until the Sync line is asserted. The Sync line may be asserted by a
direct command or by any E1439 that encounters a trigger condition and is programmed to assert
the Sync line. When the Sync signal is asserted, all modules synchronously move to the Measure
state.
In the Measure state, the E1439 continues collecting data and sends the data saved in the FIFO
memory to the selected I/O port, starting with the sample indicated by the trigger arrival, offset by
the number of samples specified by the trigger delay. This data transfer continues until all data has
been transferred or until the module meets the criteria for returning to the Idle state imposed by
block mode or continuous mode operation constraints.
IDLE ARM
Measure Trigger
Assert
Release
(Block Mode)
Release
Assert
No data collected
Old data available
Data collected and output
New data collected
Old data cleared
Data collected
Pre-trigger data cleared