IEEE-488 Bus Overview D-7
Uniline commands
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 direc-
tion 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 opera-
tion. When REN is true, devices will be removed from the local mode. Depending on device
configuration, all front panel controls except the LOCAL key (if the device is so equipped) may
be locked out when REN is true. Generally, REN should be sent before attempting to program
instruments over the bus.
EOI (End or Identify) — EOI is used to positively identify the last byte in a multi-byte
transfer sequence, thus allowing data words of various lengths to be transmitted easily.
Table D-1
IEEE-488 bus command summary
Command type Command
State of
ATN line
Comments
Uniline
Multiline
Universal
Addressed
Unaddressed
Common
SCPI
REN (Remote Enable)
EOI (End Or Identify)
IFC (Interface Clear)
ATN (Attention)
SRQ (Service Request)
LLO (Local Lockout)
DCL (Device Clear)
SPE (Serial Poll Enable)
SPD (Serial Poll Disable)
SDC (Selective Device Clear)
GTL (Go To Local)
UNL (Unlisten)
UNT (Untalk)
–
–
X
X
X
Low
X
Low
Low
Low
Low
Low
Low
Low
Low
High
High
Set up devices for remote operation.
Marks end of transmission.
Clears interface.
Defines data bus contents.
Controlled by external device.
Locks out local operation.
Returns device to default conditions.
Enables serial polling.
Disables serial polling.
Returns unit to default conditions.
Returns device to local.
Removes all listeners from the bus.
Removes any talkers from the bus.
Programs IEEE-488.2 compatible
instruments for common operations.
Programs SCPI compatible instruments for
particular operations.
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