Specifications

Read Variables Directly To directly read algorithm variables that are not stored in the FIFO or CVT, simply
specify the memory space (algorithm name or globals) and the name of the variable.
To read the values of scalar variables or single array elements, use the command
ALG:SCALar?. To read an entire array, use ALG:ARRay? The former returns
data in ASCII and the later returns data in REAL,64 (8-byte IEEE-754 format).
This coincides with the ALG:SCAL and ALG:ARR commands form writing data to
these variables. Here are some examples:
ALG:SCAL? ‘globals’,’my_var’
ALG:SCAL? ‘alg1’,’my_array[6]’
ALG:ARR? ‘alg2’,’my_other_array’
The ALG:ARR? response data will consist of a block header and real-64 data bytes.
For example, if my_other_array was 10 elements, the block header would be #280
which says there are two bytes of count that specify 80 bytes of data to follow.
Data from the VT1419A is terminated with the GPIB EOI signal.
Which FIFO Mode? The way the FIFO will be read depends on how the mode was set in the
programming step “Setting the FIFO Mode” on page 76.
Continuously Reading the FIFO (FIFO mode BLOCK)
To read the FIFO while algorithms are running, the FIFO mode must be set to
SENS:DATA:FIFO:MODE BLOCK. In this mode, if the FIFO fills up, it stops
accepting values from algorithms. The algorithms continue to execute, but the latest
data is lost. To avoid losing any FIFO data, the application needs to read the FIFO
often enough to keep it from overflowing. Here’s a flow diagram to show where
and when to use the FIFO commands.
Programming the VT1419A Multifunction
Plus
Retrieving Algorithm Data
Chapter 3 83
Begin Data Retrieval
Algorithm Stopped?
Enough Values
in FIFO?
Execute Bulk Transfer
Command
Execute Final Transfer
Command
Exit Data Retrieval
Any Values in FIFO?
no
yes
no
yes
DATA:FIFO:COUNT?
DATA:FIFO:PART? <n_values>
STAT:OPER:COND?
(bit 4 “measuring”)
no
yes
Figure 3-10: Controlling Reading Count
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