Calibrator
How to Use Commands
19
Types of Commands
The Calibrator can group commands into one or more categories, depending on how they function.
Each category is described below.
Device-Dependent Commands
Device-dependent commands are unique to the Calibrator. An example of a device-dependent
command is,
OUT 100 V, 1 A, 60 HZ
this instructs the Calibrator to source 100 watts of ac power.
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 * (asterisk) character. Common commands are available
whether you use the IEEE-488, USBTMC, RS-232 or Ethernet interface for remote control. An example
of a common command is,
*IDN?
this instructs the Calibrator to return the instrument identification string.
Query Commands
Query commands request information, which is returned as the command executes (RS-232/Ethernet),
or placed in a buffer until requested (GPIB/USBTMC). An example of a query, which always end with a
question mark, is,
RANGE?
this instructs the Calibrator primary and secondary (if in dual output mode) range values.
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.)
Note that interface messages, unlike device-dependent and common commands, 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 9 lists the interface messages that the
Calibrator accepts. Table 10 lists the interface messages that the Calibrator sends. The interface
messages that the Calibrator sends are also listed. The mnemonics listed in the tables are not sent as
literal 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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