Keithley 486 Instruction Manual page 225

APPENDME
IEEE-488 Bus
Gvervim
Table E-l. IEEE-488 Bus Command Summa~~~
We
Uniline
J,uiline
universal
Addressed
Unaddressed
Device-
dependent
Command
RZN (Remote Enable)
EOI
EC (Interface Clear)
ATN (Attention)
SRQ
LLO (Local Lockout)
DCL (Device Clear)
SPE (Serial Enable)
SPD (Serial Poll Disable)
SDC (Selective Device Clear)
GTL (Go To Local)
TJNL mllisten)
UNT Wntalk)
scription of each command. Each command is sent by set-
ting the corresponding bus line true.
REN (Remote Enable) - RFN is sent to set up instx-~~-
mats on the bus for remote operation. When REN is
true, devices will be removed from the local mode. De-
pending on device configuration, all front panel controls
except the LOCAL button (if the device is so equipped)
may be locked out when RBN is true. Generally, REN
shouldbesent beforeattemptingtoprograminstruments
over the bus.
EOI (End or Identify) -EOI is used to positively identify
the last byte in a multi-byte aansfer sequence, thus al-
lowing data words of various lengths to be tmnsmilted
&Sily.
IFC (Interface Clear) - IFC is used to clear the interface
and return all devices to the talker and listener idle states.
State
of
Al-N
Line)
X
::
Low
X
Low
J.av
Low
LOW
Low
LOW
LOW
Low
High
comments
Sets up devices for remote op-
eration.
Marks and of transmission.
Clears interface
Defines data bus contents.
Controlled by external device.
Locks out local operation.
Returns device to default condi-
tions.
Enables serial polling.
Disables serial polling.
Returns unit to default condi-
tions.
Returns device to local.
Removes all listeners from bus.
Removes any talkers from bus.
Rograms Model 486/487 for
various modes.
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 Multiline
Commands
Universal commands are those m&line commands that
require no addressing. All devices equipped to bnple-
ment such commands will do so simultaneously when
the commands is transmitted. As with all multiline com-
mands, these commands are transmitted with ATN true.
LLO (Local Lockout) - LLO is sent to the instrument to
lock out the LOCAL key and thus aU 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.
E-4