Model 7002Switch System Instruction Manual - Advanced Test ...

IEEE-488 Bus OverviewLAG (Listen Address Group) — These listen commands arederived from an instrument’s primary address and are used toaddress devices to listen. The actual command byte isobtained by ORing the primary address with $20.Common commandsCommon commands are commands that are common to alldevices on the bus. These commands are designated anddefined by the IEEE-488.2 standard.TAG (Talk Address Group) — The talk commands arederived from the primary address by ORing the address with$40. Talk commands are used to address devices to talk.SCG (Secondary Command Group) — Commands in thisgroup provide additional addressing capabilities. Manydevices (including the Model 7002) do not use thesecommands.Unaddress commandsThe two unaddress commands are used by the controller toremove any talkers or listeners from the bus. ATN is truewhen these commands are asserted.UNL (Unlisten) — Listeners are placed in the listener idlestate by the UNL command.UNT (Untalk) — Any previously commanded talkers will beplaced in the talker idle state by the UNT command.Generally, these commands are sent as one or more ASCIIcharacters that tell the device to perform a commonoperation, such as reset. The IEEE-488 bus treats thesecommands as data in that ATN is false when the commandsare transmitted.SCPI commandsSCPI commands are commands that are particular to eachdevice on the bus. These commands are designated by theinstrument manufacturer, and are based on the instrumentmodel defined by the Standard Commands for ProgrammableInstruments (SCPI) Consortium’s SCPI standard.Generally, these commands are sent as one or more ASCIIcharacters that tell the device to perform a particular operation,such as setting a range or closing a relay. The IEEE-488bus treats these commands as data in that ATN is false whenthe commands are transmitted.Command codesCommand codes for the various commands that use the datalines are summarized in Figure D-3. Hexadecimal and thedecimal values for the various commands are listed in TableD-2.D-6