Remote Operation
Using Commands
5
5-27
5-26. Common Commands
Common commands are defined by the IEEE 488.2 standard and are common to most
bus devices. Common commands always begin with an * character. Common commands
are available whether you are using the IEEE-488 or RS-232 interface for remote
control. An example of a common command is,
*IDN?
instructing the Calibrator to return the instrument identification string.
5-27. Query Commands
Query commands request information, which is returned as the command executes, or
placed in a buffer until requested. An example of a query, which always ends with a
question mark, is,
RANGE?
returning the Calibrator primary and secondary outputs.
5-28. Interface Messages (IEEE-488)
Interface messages manage traffic on the IEEE-488 interface bus. Device addressing and
clearing, data handshaking, and commands to place status bytes on the bus are all
directed by interface messages. Some of the interface messages occur as state transitions
of dedicated control lines. The rest of the interface messages are sent over the data lines
with the ATN signal true. (All device-dependent and common commands are sent over
the data lines with the ATN signal false.)
An important thing to note about interface messages is that unlike device-dependent and
common commands, interface messages are not sent literally (in a direct way). For
example, when you send a device-dependent query to the Calibrator, the controller
automatically sends the interface message MTA (My Talk Address).
IEEE-488 standards define interface messages. Table 5-4 lists the interface messages
that the Calibrator accepts. Table 5-4 also shows the BASIC statement to generate the
interface message. Table 5-5 lists the interface messages that the Calibrator sends. The
mnemonics listed in the tables are not sent in BASIC PRINT statements as commands
are; in this way they are different from device-dependent and common commands.
Interface messages are handled automatically in most cases. For example, handshake
messages DAV, DAC, and RFD automatically occur under the direction of an
instrument’s interface itself as each byte is sent over the bus.
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