Output Formats; State Storage And Program Memory - Agilent Technologies 3458A User Manual

storage. The transfer rate into and out of the Reading Memory and the GPIB
transfer rate using direct memory access with an HP 9000 Series 200/300
computer is 100,000 readings per second. The advantage of the memory is that
one may access the data when it is convenient for the controller and not have to
tie the system up waiting for the measurement to finish (a long integration period,
a long settling time, or an average of multiple readings can cause even the fastest
dmm to hold up the system).

Output Formats

The 3458A offers five different data formats for both memory and GPIB output:
single integer (SINT), double integer (DINT), IEEE-728 four byte single real
(SREAL), IEEE-728 eight byte double real (DREAL), and ASCII. The fastest
format for data transfer is the single integer. This is a 16 bit integer format so
range information must be known to determine the placement of the decimal point.
In addition, it only has 16 bits; hence, if more than 4 1/2 digits is desired from a
measurement, one of the other formats must be used. The next highest speed
format is double integer. This is a 32 bit integer format so, except for the range
information, all the measurement data is transferred. SREAL transfers all the
data, including the range information, in four eight-bit bytes. The controller must
be able to accept this format and translate it into ASCII to be able to use it. Finally,
the slowest format is the ASCII format. Basically, each reading needs eighteen
bytes of data plus carriage return/ line feed terminator to transfer into the
controller. Many times it is important to acquire the data quickly but the actual
transfer of the data can be comparatively slow, In this case, the ideal combination
of data formatting is SREAL for measurements taken into memory and ASCII
output to GPIB. The DINT and SINT formats are accepted directly without need
for additional translation by the HP 9000 Series 200/300 computers. Almost any
controller can accept ASCII formats.
In programs where functions or ranges are changed between measurement and
the results are stored in the computer, it is probably best to lose a little speed and
store the data in Reading Memory in either DREAL or SREAL. This avoids having
to keep track of the scaling parameters needed for SINT and DINT.
State Storage and
A considerable savings in time at the right place in the testing task may be gained
by the features of State Storage and Program Memory. State memory is used to
Program Memory
establish a static state of the instrument with a single command transfer over GPIB.
Initialization routines can set up the states that the programmer wishes to use in
the test program during system dead time; then the state can be called at will.
Program Memory is dynamic memory. The state of the 3458A is dynamically
changed as the sequence of operations programmed in Program Memory are
stepped through as though the computer were controlling the sequence of events.
The measurements taken can be stored in Reading Memory to be accessed at a
convenient time either to be transferred in raw form to the computer or to be post
processed in the 3458A. Again, once the command string is transferred to the
memory of the 3458A, a simple command over GPIB initiates the measurement
sequence. More important than the time saved by passing the simple command,
the parsing routine of the 3458A actually compiles the Program Memory
command string so that the measurement sequence can take place much faster
than if the computer were controlling the operation. To ease some of the
programming burden for lengthy set-ups, State Memory and other subprograms
may be called from Program Memory.
Appendix D Optimizing Throughout and Reading Rate 331