IEEE-488 Bus Overview
A-4
* See Section 3 for a complete description of device-dependent commands.
Table A-1
IEEE-488 bus command summary
Command type
Command
Comments
Uniline
REN (Remote
Enable)
EOI
(End or Identify)
IFC (Interface
Clear)
ATN (Attention)
SRQ (Service
Request)
Set up for remote operation.
Marks end of transmission.
Clears interface.
Defines bus contents.
Device requesting service.
Multiline
Universal
Addressed
Unaddressed
LLO (Local
Lockout)
DCL (Device
Clear)
SPE
(Serial Poll Enable)
SPD
(Serial Poll Disable)
SDC
(Selective Device Clear)
GTL (Go
To
Local)
GET (Group
Execute
Trigger)
UNL
Unlisten
UNT (Untalk)
Locks out front panel controls.
Returns device to default conditions.
Enables serial polling.
Disables serial polling.
Returns to default conditions.
Cancels remote state.
Triggers device for reading.
Removes all listeners from bus.
Removes talker from bus.
Device-dependent*
Programs Model 6512 operating modes.
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 direction
of data transfer. The following is a description of each com-
mand. 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 operation. Generally, REN should be as-
serted 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.
IFC (Interface Clear)—IFC is used to clear the interface and
return all devices to the talker and listener idle states.
ATN (Attention)—The controller asserts ATN while trans-
mitting addresses or multiline commands.
SRQ (Service Request)—SRQ is asserted by a device when
it requires service from a controller.
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 Lockout)—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 pow-
er-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.
Summary of Contents for 6512
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