12-5
IM GS210-01EN
GP-IB Interface
12.5 Responses to Interface Messages
What Are Interface Messages?
Interface messages are also referred to as interface commands or bus commands. They
are commands that are issued by the controller. They are classified as follows:
Uni-line Messages
A single control line is used to transmit uni-line messages. The following three types of
messages are available.
IFC (Interface Clear), REN (Remote Enable), and IDY (Identify)
Multi-line Messages
Eight data lines are used to transmit multi-line messages. The messages are classified
as follows:
• Address Commands
These commands are valid when the instrument is designated
as a listener or as a
talker. The following five commands are available.
• Commands that are valid on an instrument that is designated
as a listener
GTL (Go To Local), SDC (Selected Device Clear), PPC (Parallel Poll Configure),
and GET (Group Execute Trigger)
• A
command that is valid on an instrument that is designated as a talker
TCT (Take Control)
• Universal Commands
These commands are valid on all instruments regardless of their listener or talker
designation. The following five commands are available.
LL
O (Local Lockout), DCL (Device Clear), PPU (Parallel Poll Unconfigure), SPE (Serial
Poll Enable), and SPD (Serial Poll Disable)
Other Interface Messages
Listener address, talker address, and secondary commands are also considered
interface messages.
Difference between SDC and DCL
In multi-line messages, SDC messages are those that require talker or listener
designation and DCL messages are those that do not require a designation. Therefore,
SDC messages are directed at a particular instrument while DCL messages are directed
at all instruments on the bus.
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