VXI VT1422A, VT1529A/B Selecting the FIFO Mode,

128 Programming the VT1422A for Data Acquisition and Control Chapter 4
To specify that values are to remain in IEEE 32-bit Floating Point format for
fastest transfer rate:
FORMAT REAL,32
To specify that values are to be converted to 7-bit ASCII and returned as a
fifteen character per value comma separated list:
FORMAT ASC,7 The *RST, *TST?, and power-on
default format
or
FORM ASC same operation as above
Selecting the
FIFO Mode
The VT1422A’s FIFO can operate in two modes. One mode is for reading
FIFO values while the VT1422A is scanning and/or running algorithms; the
other mode is for reading FIFO values after operation have been halted
(ABORT sent).
• BLOCking: The BLOCking mode is the default and is used to read the
FIFO while algorithms are executing. The application program must
read FIFO values often enough to keep it from overflowing (See
“Continuously Reading the FIFO (FIFO mode BLOCK)” on page135.).
The FIFO stops accepting values when it becomes full (65,024 values).
Values sent after the FIFO is full are discarded. The first value to
exceed 65,024 sets the STAT:QUES:COND? bit 10 (FIFO Overflowed)
and an error message is put in Error Queue (read with SYS:ERR?
query).
•OVERwrite: When the VT1422A is running and the FIFO fills, the
oldest values in the FIFO are overwritten by the newest values. Only
the latest 65,024 values are available. In OVERwrite mode the module
must be halted (ABORT sent) before reading the FIFO (See “Reading
the Latest FIFO Values (FIFO mode OVER)” on page137.).
This mode is very useful when viewing an algorithm’s response to a
disturbance is desired.
To set the FIFO mode (blocking is the *RST/Power-on condition):
[SENSe:]DATA:FIFO:MODE OVERWRITE select overwrite mode
[SENSe:]DATA:FIFO:MODE BLOCK select blocking mode