G-4 488.1 Protocol
Using SCPI-based programs
In general, an existing SCPI-based program will run properly and faster in the 488.1 protocol
as long as it meets the previous 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.
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 power supply will automatically assume a read query 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. For the Models 2306, 2306-VS, and
2306-PJ, trigger on talk applies to the active channel (DISP:CHAN?). If active channel is
channel 1, then it assumes a READ1?, or else if channel 2 is active, then READ2?.
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 timeouts when using SRQ on MAV for queries that
take a long time to execute.
General operation notes
• The remote blinking R on the front panel still operates since it is critical to fundamental
GPIB operation.
• If the unit is in REMote, the GTL command may not put the power supply into the local
mode. Only the front pane
l LOCAL key is guaranteed to operate, if not in local lockout
(LLO). GTL will still disable LLO.
• IEEE-488 bus commands and features (GET, IF
C, SDC, DCL, LLO, Serial Poll, and
SRQ) are still fully supported.
• Multiple TALKs on the same query are supported as in the SCPI protocol. This feature
is
useful when reading back long ASCII strings.
Test Equipment Depot - 800.517.8431 - 99 Washington Street Melrose, MA 02176
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