User manual

ATN, IFC and REN are asserted only by the controller. SRQ is asserted by an external
device. EOI may be asserted either by the controller or other devices depending on the di
-
rection of data transfer. The following is a description of each command. Each command is
sent by setting the corresponding bus line true.
REN (Remote Enable) — REN is sent to set up instruments on the bus for remote oper-
ation. When REN is true, devices will be removed from the local mode. Depending on device
con used to positively identify the last byte in a multi-byte transfer sequence, thus allowing
data words of various lengths to be transmitted easily.
IFC (Interface Clear) — IFC is used to clear the interface and return all devices to the talk-
er and listener idle states.
ATN (Attention) — The controller sends ATN while transmitting addresses or multiline
commands.
SRQ (Service Request) — SRQ is asserted by a device when it requires service from a
controller.
Universal commands are those multiline commands that require no addressing. All devic-
es equipped to implement such commands will do so simultaneously when the commands
are transmitted. As with all multiline commands, these commands are transmitted with ATN
true.
LLO (Local Lockout) — LLO is sent to the instrument to lock out the LOCAL key and thus
all 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 (Serial 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 all devices on the
bus from the serial poll mode and is generally the last command in the serial polling se-
quence.
IEEE-488 Bus Overview E-9
2000-900 (J - Aug 2010) BOOK.fm Page 9 Wednesday, October 12, 2011 12:29 PM