Specifications

As stated earlier in the chapter, all updates (changes) are held in a holding buffer
until the computer issues the update command. The ALG:UPD is that command.
Executing ALG:UPD before INIT does not make much difference since there is no
concern as to how long it takes or how it is implemented. After INIT forces the
buffered changes to all take place during the next Update Phase in the trigger cycle
after reception of the ALG:UPD command.
Defining Data Storage
Specifying the
Data Format
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 Same as REAL,64 except for the values of IEEE,
-INF, IEEE +INF and Not-a-Number (NaN). See
FORMat command in Chapter 5 for details.
REAL,32 means real 32-bit (no conversion, fastest)
REAL same as above
REAL,64 means real 64-bit (values converted)
ASCii,7 means 7-bit ASCII (values converted)
ASCii same as above (the *RST condition)
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 The *RST, *TST?, and power-on
default format
or
FORM ASC same operation as above
Turning Off IEEE ± INF
and NaN Values
The VT1419A stores data in its FIFO and CVT in a data format adhering to the
IEEE-754. This format yields ±INF and NaN numbers for those values that
indicate an out-of-bound condition (overrange reading) or some uninitialized
number (CVT element has not been written), respectively. Normal data queries for
Agilent VEE do not permit these numbers to go unnoticed during a transaction.
Agilent VEE makes certain that valid numbers are being dealt with to avoid making
calculations that can eventually cause errors. Therefore, any transaction that
involves these numbers will cause an error in Agilent VEE and will abort the
transaction.
To avoid this condition, the VT1419A SCPI command DIAG:IEEE OFF can be
issued to the VT1419A to force it to never output ±INF or NaN. The default
power-on or *RST condition is DIAG:IEEE ON, so this command must be
explicitly sent to avoid the condition. Keep in mind that this condition ONLY
occurs when selecting the FORM REAL command. FORM PACKED is another
Programming the VT1419A Multifunction
Plus
Defining Data Storage
Chapter 3 75
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