6482-901-01 Rev. A / August 2012
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E-3
Model 6482 Dual-Channel Picoammeter / Voltage Source Reference Manual
Appendix E: GPIB 488.1 Protocol
For example, the following command strings are invalid:
:SOUR2:VOLT:RANG 10;*OPC?
:SENS2:CURR:RANG?;:READ?
:READ?;:READ?
The following command strings are valid:
:SOUR1:VOLTage:STARt 1;STOP 10;step 1
:curr:nplc 1.0;:curr:rang min
:SENS2:CURR:RANG? MAX
:READ?
•
When a query is sent, either the data must be read back or a Device Clear (DCL) or
Interface Clear (IFC) must be performed to reset the query.
•
When sending a command or query, do not attempt to read data from the Model 6482 until
the terminator has been sent (usually Line Feed with EOI). Otherwise, a DCL or IFC must
be sent to reset the input parser.
•
When receiving data, all data, up to and including the terminator (LF with EOI), must be
accepted. Otherwise, a DCL or IFC must be sent to reset the output task.
•
Empty command strings (terminator only) should not be sent.
Using SCPI-based programs
In general, an existing SCPI-based program will run properly and faster in the 488.1 protocol if it
meets the above guidelines and limitations.
Bus hold-off
*OPC, *OPC?, and *WAI are still functional but are not needed for the 488.1 protocol. When
sending commands, the GPIB is automatically held off when it detects a terminator. The hold-off is
released when all the commands have finished executing, or if there is some parser or command
error. An exception is an initiate command, which releases the hold-off immediately and does not
wait for all of the readings to be acquired. This immediate release of bus hold-off is done to
support GET, SDC, IFC, *TRG, *RCL, *RST, SYSTem:PRESet and ABORt during data acquisition.
Trigger-on-talk
Trigger-on-talk functionality has been added for the 488.1 protocol. If a query has not been
received by the instrument, the Model 6482 will automatically assume a READ? command has
been sent when it is addressed to talk. This technique increases GPIB speed by decreasing the
transmission and parser times for the command.
Trigger-on-talk is extremely useful in the single-shot reading mode (*RST default) and is the main
reason for a >2x speed improvement over the SCPI protocol. Remember that the output must be
on (:OUTPut[1]:STATe ON or :OUTPut2:STATe ON) before you can take readings.
The ARM:SOUR BUS and ARM:COUN INF commands are not supported by READ? with the
488.1 protocol selected. If you send one of these commands, a DCL or IFC may be required to
reset the GPIB.
Message available
The MAV (message available) bit in the Serial Poll byte will be set when the query is finished being
processed, not when there is data available in the output buffer (as with the SCPI protocol). For
the 488.1 protocol, output data will not be formatted until the first request for data is received. This
delay may cause unexpected time-outs when using SRQ on MAV for queries that take a long time
to execute.
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