VXI VT1433B - Manual (Page 99)

Upon entering the ARM state the VT1433B starts saving new data in its FIFO.
It remains in the ARM state until the Sync/Trigger line goes high. If the
VT1433B is programmed with a pre-trigger delay, it collects enough data samples
to satisfy this pre-trigger delay and then releases the Sync/Trigger line. If no
pre-trigger delay has been programmed, it releases the Sync/Trigger line
immediately. When all modules in a system have released the Sync/Trigger line
(allowing it to go high), a transition to the TRIGGER state occurs.
Upon entering the TRIGGER state the VT1433B continues to collect data into the
FIFO, discarding any data prior to the pre-trigger delay. The VT1433B remains
in the TRIGGER state until it sees a high-to-low transition of the Sync/Trigger
line. The Sync/Trigger line is pulled low by any VT1433B which encounters a
trigger condition and is programmed to pull the Sync/Trigger line. If any
VT1433B is programmed for auto triggering (with e1432_set_auto_trigger), the
Sync/Trigger line is pulled low immediately. The Sync/Trigger line may also be
pulled low by an explicit call to the function e1432_trigger_measure.
Upon entering the MEASURE state the VT1433B continues to collect data. The
VT1433B also presents the first data from the FIFO to the selected output port,
making it available to the controller to read. The VT1433B holds the
Sync/Trigger line low as long as it is actively collecting data. In overlap block
mode the VT1433B stops taking data as soon as a block of data has been
collected, including any programmed pre- or post-trigger delays. (It starts again
when another trigger occurs). In continuous mode, the VT1433B stops taking
data only when the FIFO overflows. When data collection stops, the VT1433B
releases the Sync/Trigger line. When all VT1433Bs are finished and the
Sync/Trigger line goes high, the VT1433B goes into the IDLE state again.
The measurement initialization and loop may be interrupted at any time with a
call to e1432_reset_measure, which puts the module in the TESTED state.
Register-based VXI Devices
The VT1433B is a register-based VXI device. Unlike message-based devices
which use higher-level programming using ASCII characters, register-based
devices are programmed at a very low level using binary information. The
greatest advantage of this is speed. Register-based devices communicate at the
level of direct hardware manipulation and this can lead to much greater system
throughput.
It is not necessary to access the registers to use the VT1433B. The VT1433B’s
functions can be more easily accessed using the VT1432A Host Interface Library
software. However, if information about the registers is provided see
Appendix A: Register Definitions for reference.
VT1433B User's Guide
The Host Interface Library
4-21