Model 6485 Picoammeter Instruction Manual IEEE-488 and SCPI Conformance Information G-5
Message exchange protocol (MEP)
When the 488.1 protocol is selected, the MEP is disabled to speed up GPIB operation.
The following guidelines/limitations must be followed when using the 488.1 protocol:
• If a query is sent, it must be the only command on the line (this limitation also
means no multiple queries can be sent). Otherwise, full SCPI command syntax is
still supported including long-form and short form commands, multiple com-
mands, and MIN/MAX/DEF parameter definitions.
For example, the following command strings are invalid:
:CURR:RANG .020; *OPC?
:CURR:RANG?;: READ?
:READ?;:READ?
The following strings are valid:
curr:nplc 1.0;:curr:rang min
: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
6485 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 pro-
tocol as long as it meets the above guidelines and limitations.
NRFD 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 imme-
diate release of bus hold-off is done to support GET, SDC, IFC, *TRG, *RCL, *RST,
SYSTem:PRESet, and ABORt during data acquisition.
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