Store the Readings in
Command Module
RAM Instead of
Sending them Directly
to the Computer
There is a major difference between
INIT;:FETCH?
and
READ?
after a
CONFigure
command.
INIT;:FETCH?
When the
INITiate
command is sent to the HP E1326B, the multimeter will
reserve four bytes per reading of command module RAM to hold the total
number of readings that the E1326B multimeter has been configured to
take. For example:
CONF:VOLT:DC?
SAMP:COUNT 1000
INIT
!
Reserves room for 1000 four
byte readings
FETCH?
The HP E1326B then takes the readings as soon as its trigger conditions
have been satisfied. For example, if the trigger source is
IMMediate
, the
readings are started once
INITiate
is executed. If the trigger source is
BUS
,
then the readings are started when a group execute trigger is received.
The
FETCH?
command causes the readings that have been stored in the
HP E1300/E1301 RAM (or command module RAM) to be retrieved and sent
over the HP-IB bus. No readings are output until all readings have been taken
and stored in RAM. This results in a burst-then-transfer mode of operation.
This mode of operation has been designed so that readings from the E1326B
multimeter can be received and placed into RAM at any reading rate up to
13 kHz. The 13 kHz rate is achieved with auto zeroing and auto ranging
OFF, and the 10
µ
s aperture time selected. In this mode, the E1326 does a
two-pass process on the data. In response to the
INIT
command, the
multimeter readings are placed into RAM in the multimeter’s internal
format as they are taken. When the first pass ends, the readings in RAM are
converted to 32-bit REAL numbers. The
FETCH?
command outputs the
readings in the format that has been selected.
The maximum number of readings is limited by the amount of RAM in the
HP E1300/E1301 mainframe or command module. The RAM is used up at
the rate of four bytes per reading.
Appendix D
Measurement Speed and Accuracy Tradeoffs 277
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