GPIB 488.1 Protocol G-5
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 6430 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 out-
put must be on (:OUTput: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 fin-
ished 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 que-
ries that take a long time to execute.
General operation notes
• The TALK, LSTN, and SRQ annunciators are not functional in the 488.1 protocol. This
speeds up data through-put greatly. The REM annunciator still operates since it is criti-
cal to fundamental GPIB operation.
• If the unit is in REMote, the GTL command may not put the Model 6430 into the local
mode. Only the front panel LOCAL key is guaranteed to operate, if not in local lockout
(LLO). GTL will still disable LLO.
• IEEE-488 bus commands and features (GET, IFC, 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.
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