IFC (Inter&z Clear)-IFC is used to clear the interface and
return all devices to the talker and listener idle states.
ATN (Attention)-The controller sends ATN while transmit-
ting addresses or multiline commands.
SRQ (Service Request)-SRQ is asserted by a device when it
requires service from a controller.
3.4.2 Universal Commands
Universal commands are those multiline commands that re-
quire no addressing. All devices equipped to implement such
commands will do so simultaneously when the command is
transmitted. As with all multiline commands, these com-
mands are transmitted with ATN true.
LLO (Local Lockou+LLO is sent to instruments to lock out
their front panel controls.
DCL (Device Clear)-DCL is used to return instruments to
some default state. Usually, instruments return to their
power-up conditions.
SPE 6xial Poll Enable)-SPE is the first step in the serial
polling sequence, which is used to determine which device has
requested service.
SPD (Serial Poll Disable)-SPD is used by the controller to
remove a11 devices on the bus from the serial poll mode and is
generally the last command in the serial polling sequence.
3.4.3 Addressed Commands
Addressed commands are multiline commands that must be
preceded by the devici listen address before that instrument
will respond to the command in question. Note that only the
addressed device will respond to these commands:
SDC (Selective Device Clear)-The SDC command performs
essentially the same function as the DCL command except
that only the addressed device responds. Generally, in-
struments return to their power-up default conditions when
responding to the SDC command.
GTL (Go To Local&The GTL command is used to remove
instruments from the remote mode. With some instruments,
GTL also unlocks front panel controls if they were previously
locked out with the LLO command.
GET (Group Execute Trigger)-The GET command is used to
trigger devices to perform a specific action that depends on
device configuration (for example, take a reading). Although
GET is an addressed command, many devices respond to
GET without addressing.
Table 3-l. IEEE-488 Bus Command Summaw
State of
Command Type Command
ATN Line” Comments
Uniline REN (Remote Enable)
X Set up for remote operation.
EOI
X Marks end of transmission.
IFC (Interface Clear)
X Clears Interface
ATN (Attention)
LOW Defines data bus contents.
SRQ
X Controlled by external device.
Multiline
Universal LLO (Local Lockout)
Low
Locks out front panel controls.
DCL (Device Clear)
Low
Returns device to default conditions.
SPE (Serial Poll Enable)
LOW Enables serial polling.
SPD (Serial Poll Disable)
LOW Disables serial polling.
Addressed SDC (Selective Device Clear) !
LOW Returns unit to default conditions.
GTL (Go To Local)
LOW Sends go to local.
GET (Group Execute Trigger)
Low Triggers device for reading.
Unaddressed UNL (Unlisten)
Low
Removes all lineners from bus.
UNT Wntalk)
LOW
Removes any talkers from bus.
Device-dependent”*
High Programs Model 617 for various modes.
*Don’t Care.
**See paragraph 3.10 for complete description.
34
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