GPIB
4-4 370B User Manual
Interface messages are commands that control interface functions. The IEEE 488
standard specifies interface message so that they are the same for all devices.
There are two kinds of interface messages: uni-line and multi-line, where “line”
refers to the 16 signal lines within the bus. Multi-line messages can be further
subdivided into universal commands, addresses, and addressed commands.
Figure 4–2 shows how the different types of GPIB messages are related and
indicates the standard three-letter symbols assigned to them.
Multi-line interface messages are sent by placing a byte on the eight data lines of
the GPIB and asserting the ATN line. Universal commands affect all devices on
the bus while addresses and addressed commands affect only the addressed
instruments.
Figure 4-2: GPIB message types
Uni-line interface messages are sent by asserting one of the five individual
interface signal lines of the GPIB:
SRQ (service request)
ATN (attention)
IFC (interface clear)
REN (remote enable)
END (EOI, end or identify)
Device-dependent messages consist of commands or data that control instrument
function and communicate instrument status, as well as data from measurements
and other information. As noted before, the content and format of these messages
has been addressed with Tektronix Codes and Formats. All of these message
types are significant for the 370B.
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