APPENDIX C
Figure C-2. IEEE Handshake Sequence
BUS COMMANDS
Commands associated with the IEEE-488 bus can be
grouped into the following three general categories. Refer
to Table C-l.
IJniIine CommandsThese commands are asserted by set-
ting the associated bus line true. For example, to assert
REN (Remote Enable), the REN line would be set low
&W.
MultiIine Commands-General bus commands which are
sent over the data lines with the ATN line true.
Device-dependent Commands-Commtids whose mean-
ings depend on the device in question. These commands
are transmitted via the data lines while ATN is false.
Table C-l. IEEE-488 Bus Command Summary
State of
Command Type
Command
ATN Lie* Comments
Uniline
REN (Remote Enable)
X Sets up devices for remote operation.
EOI
X Marks end of transmission.
IFC (Interfack Clear)
X Clears Interface.
AIN (Attention)
Low
Defines data bus contents.
SRQ
X
Controlled by external device.
Multiline
Universal
iL0 (Local Lockout)
Low Locks out local operation.
DCL (Device Clear)
Low
Returns device to default conditions.
SPE (Serial Enable)
Low
Enables serial polIing.
SPD (Serial PoU Disable)
Low Disables serial polling.
Addressed
SDC (Selective Device Clear)
Low Returns unit to default conditions.
GTL (Go To Local)
IDN Returns device to local.
GET (Group Execute Trigger)
Low Triggers device for reading.
Unaddressed
UNL (Unlisten)
Low Removes all listeners from bus.
UNT (Untalk)
Low Removes any talkers from bus.
Device-dependent
High
Programs Model 199 for various modes.
*Don’t Care.
c-3
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