Tektronix 2714, Programmer'S Manual

Page: 47 / 308

Instrument-Specific Message Structure
2714 & 2715 Programmer Manual
2–7
HARD flow control, the default method, uses the RTS (Request To Send) and
CTS (Clear To Send) handshake lines. In this mode the remaining output line,
DTR (Data Terminal Ready), is always asserted TRUE and input lines DCD
(Data Carrier Detect) and DSR (Data Set Ready) are ignored.
SOFT flow control uses the CTRL-Q/CTRL-S method. Output lines RTS and
DTR are always asserted TRUE and input lines DCD, CTS, and DSR are
ignored. This method should not be specified for binary transfers such as
waveforms or files.
NONE (no flow control) may also be specified. In this case the user is responsi-
ble to ensure that I/O buffers do not overflow. Note that both SOFT flow control
or NONE (no flow control) allow the use of a 3-wire interface (GND, TXD, and
RXD). In each case RTS and DTR are asserted TRUE and the CTS, DCD, and
DSR inputs are ignored. Refer to Appendix A for more details on RS-232
connector wiring and the implementation of the interface standard by the 2714 or
2715.
Message Buffering (GPIB)
The 2714 or 2715 Spectrum Analyzer with Option 03 (GPIB) buffers each input
message that it receives. Message processing begins as soon as messages are
received by the 2714 or 2715; it does not wait for the message terminator. The
2714 or 2715 remains busy until it is done executing the commands in its input
buffer, unless the process is stopped by the DCL (Device Clear) or SDC
(Selected Device Clear) GPIB messages.
If an error is detected while transferring a command or query, the remainder of
the message (up to the message terminator) is discarded.
Output data is ready following execution of each query and is passed to the 2714
or 2715’s output buffer prior to transmission over the bus. The spectrum analyzer
begins to transmit an output message after it is addressed as a talker and the data
is available. However, the response terminator is not sent until the command
terminator is detected in case there are more queries in the input message.
Output continues from the 2714 or 2715 until the end of the information in the
output buffer is reached, or until it is interrupted by a DCL (Device Clear), UNT
(Untalk), or IFC (Interface Clear) GPIB message. If the 2714 or 2715 is
interrupted before the buffer is cleared, output will resume if it is readdressed as
a talker.
The buffer is cleared by the DCL or SDC messages. The 2714 or 2715 termi-
nates the output according to the selected message terminator (EOI or CR/LF/
EOI) unless it is interrupted.