Tektronix 2714, Руководство программиста

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Introduction to Programming
2714 & 2715 Programmer Manual
1–11
The programming requirements for RS-232 control are more complex than those
for GPIB operation. Programming contains a complete example of an interactive
RS-232 control program. This program is functionally similar to the GPIB
program example located later in this section (refer to A GPIB Instrument
Control Program on page 1–23).
GPIB Operation (Option 03)
Option 03 adds a General Purpose Interface Bus (GPIB) port. This GPIB port
conforms to the IEEE 488.1 Standard and to the Tektronix Interface Standard for
GPIB Codes, Formats, Conventions, and Features. This standard promotes ease
of operation and, so far as possible, makes this spectrum analyzer compatible
with other Tektronix instruments and with GPIB instruments from other
manufacturers.
The IEEE 488.1 Standard establishes electrical levels, connector configuration,
and signal protocols for communication between two or more electronic
instruments using a common multi-line bus structure. The bus structure, known
as the GPIB, consists of eight data lines, eight dedicated control signal lines, a
shield, and various grounds.
Data is transferred via eight data lines in a bit parallel, byte serial fashion. That
is, the eight bits of a data byte are placed on the eight data lines simultaneously.
As soon as they are transferred, the next 8-bit data byte is placed on the lines and
is transferred. Data consists of instrument commands and queries, control
settings, parameter values, or display information.
The eight control lines are divided into three transfer control (handshake) lines
and five interface management lines. Handshaking and interface management are
necessary because the bus operates asynchronously. This means that signals can
be generated by one instrument without regard for what other instruments may
be doing, or the rate at which other instruments can carry out an operation. For
instance, two instruments may try to send information simultaneously, or a high
speed instrument may try to send data to a slower instrument.
Instruments connected to the bus are designated as talker, listener, or both talker
and listener. A listener can only receive information over the bus and a talker can
only send information. A talker and listener can do both (but not simulta-
neously).
One instrument is usually designated as the system controller. This is generally a
computer that determines, through software, when specific instruments are
activated as talkers or listeners. Each instrument is assigned a unique address
between 0 and 30, but only 15 instruments can be connected to the bus
simultaneously.