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Defining Data Storage
Specifying the
Data Format
Selecting the
FIFO Mode
Chapter 3
The format of the values stored in the FIFO buffer and CVT never changes.
They are always stored as IEEE 32-bit Floating point numbers. The
FORMat <format>[,<length>] command merely specifies whether and how
the values will be converted as they are transferred from the CVT and FIFO
to the host computer.
•
The <format>[,<length>] parameters can specify:
PACKED
(NaN).
REAL,32
REAL
REAL,64
ASCii,7
ASCii
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
15 character per value comma separated list:
FORMAT ASC,7
or
FORM ASC
The HP E1415's FIFO can operate in two modes. One mode is for reading
FIFO values while algorithms are executing, the other mode is for reading
FIFO values after algorithms have been halted (ABORT sent).
•
BLOCking; The BLOCking mode is the default and is used to read the
FIFO while algorithms are executing. Your application program must
read FIFO values often enough to keep it from overflowing (See
"Continuously Reading the FIFO (FIFO mode BLOCK)" on
page 89.). The FIFO stops accepting values when it becomes full
(65,024 values). Values sent by algorithms 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? command).
•
Overwrite; When 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
Programming the HP E1415 for PID Control
Same as REAL,64 except for the values of
IEEE -INF, IEEE +INF, and Not-a-Number
See FORMat command in Chapter 5 for details.
means real 32-bit (no conversion, fastest)
same as above
means real 64-bit (values converted)
means 7-bit ASCII (values converted)
same as above (the *RST condition)
The *RST, *TST? and power-on
default format
same operation as above
81
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