Tektronix 2714, Руководство программиста

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Appendix B: GPIB System Concepts
2714 & 2715 Programmer Manual
B–3
Functional Elements
The functional elements of the GPIB cover three areas:
H
The ten major interface functions of the GPIB are listed in Table B–1. Each
function is a system element that provides the basic operational facility by
which an instrument can receive, process, and send messages over the GPIB.
H
The second functional element is the specific protocol by which the interface
functions send and receive their limited set of messages.
H
The logical and timing relationships between allowable states for all
interface functions is the third area covered.
Table B–1: Major GPIB Interface Functions
Interface Function Symbol
Source Handshake SH
Acceptor Handshake AH
Talker or Extended Talker T or TE
Listener or Extended Listener L or LE
Service Request SR
Remote-Local RL
Parallel Poll PP
Device Clear DC
Device Trigger DT
Controller C
Note that while the IEEE Std 488.1 standard defines the ten interface functions,
the specific protocol, and timing relationships, not every instrument on the bus
will have all ten interface functions incorporated. Only those functions important
to a particular instrument’s purpose need to be implemented.
A Typical GPIB System
A typical GPIB instrumentation system is shown in Figure B–2, and it includes
the nomenclature for the sixteen active signal lines. Only four instruments are
shown in this example, but the GPIB can support up to fifteen instruments
connected directly to the bus. However, more than fifteen devices can be
supported by a single bus if they are interfaced through a primary device. Such a
scheme can be used for programmable plug-ins housed in a mainframe where the
mainframe is addressed with a primary address code and the plug-ins are
addressed with a secondary address code.