Tektronix 2714, Programmer'S Manual

Page: 20 / 308

Introduction to Programming
1–8
2714 & 2715 Programmer Manual
NONE: No flow control is used.
Follow these general rules when selecting a flow control method:
H
Do not use SOFT flow control when transmitting file or waveform data
(binary transfers) because there is no guarantee that the ASCII-decimal
values corresponding to CTRL-S and CTRL-Q do not appear in the input
stream. Instead, specify HARD flow control or NONE for files and
waveform data.
H
If NONE is specified, you must ensure that buffers do not overflow. This can
be done by allocating enough buffer space to handle most contingencies. A
buffer size of 1200 is sufficient for most purposes. The 2714 or 2715 uses a
1200-byte, internal input buffer.
Selecting the Echo Feature.
Item 6 of the RS-232 PORT CONFIGURATION
Menu, ECHO, chooses ECHO modes of ON or OFF. ECHO mode is intended
primarily as a means of interacting with the 2714 or 2715 from a “dumb”
terminal, or for testing purposes. Press [6] on the KEYPAD to choose between
ON or OFF.
When ECHO is OFF, the spectrum analyzer does not return the characters it
receives to the controller. For most cases, ECHO should be OFF. However, set
ECHO to ON when using a “dumb” terminal to control the spectrum analyzer.
When ECHO is ON, the spectrum analyzer echoes each character it receives back
to the controller. This can cause problems for the control program if it is not
expecting the characters. Additional time is required to process each returned
character, so it is possible to experience buffer overrun at 9600 baud if the
character rate is too high. After each command or query is completed, the
spectrum analyzer prompts for further input by returning the string “>” to the
controller.
For example, if ECHO mode is ON, “>” appears on the terminal or computer
display screen. If the query “
VPO?
” is entered, the spectrum analyzer returns
“
VPO?
” followed by a normal response to the query, such as “
VPOLARITY
POSITIVE
”. It then appends the “>” to indicate that it is ready to receive
additional commands.
ECHO mode is sometimes useful for interactive testing because it lets you see
each character received by the spectrum analyzer. Following are some important
ECHO mode characteristics:
H
If SOFT flow control is enabled, CTRL-S and CTRL-Q are not echoed, but
they perform their normal functions.
H
If either CR or LF is received by the spectrum analyzer, it is echoed as the
currently selected output terminator.