Tektronix 2714, Руководство программиста

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Introduction to Programming
1–12
2714 & 2715 Programmer Manual
The following example illustrates how data transfer typically takes place (except
in the case of abnormal events; see Status Reporting).
1. The instrument on the bus that is designated as system controller determines
(through operator intervention or program control) that it needs to send a
message to one of the other instruments.
2. Using the data and interface management lines, the controller first addresses
the desired instrument as a listener. This is called LISTENING an instru-
ment.
3. Instruments on the bus are normally idle, and they signal using the hand-
shake lines when they are ready to receive data. The controller then places
the first byte of the message on the bus, indicating the type of information it
wants.
4. Next the controller signals, using the handshake lines, that the data byte is
ready.
5. As the listener accepts the data byte, it signals over the handshake lines that
it has done so. The controller then removes the data from the data lines.
6. The process from steps 3, 4, and 5 is repeated until the entire message has
been transferred.
7. The controller indicates that the last data byte has been sent. Depending on
the option selected, one of two methods is used: 1) Signaling over the end or
identify (EOI) interface management line simultaneously with the last data
byte, or 2) Appending the ASCII codes for carriage return (CR) and line feed
(LF) to the end of the message and simultaneously signaling EOI.
8. When the message is complete, the controller normally UNLISTENS the
instrument. If a message requires a response, the controller then addresses
the instrument as a talker (TALKS the instrument).
9. Now the instrument places the first byte of the response on the data bus and
signals that it is ready.
10. After the controller reads the byte, it signals (over the handshake lines) that it
has done so and is ready to receive more data. The process repeats until EOI
is detected, at which point the controller normally UNTALKS the instru-
ment.
The data transfer process is transparent to you. It is carried out by the spectrum
analyzer, the GPIB board in your controller, and the device driver software
(generally supplied with the GPIB board). In the following subsections you will
learn how to set up your spectrum analyzer for GPIB operation. See Appendix B:
GPIB System Concepts for additional information concerning IEEE 488.1 and
the GPIB.