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2714 & 2715 Programmer Manual
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Appendix A: RS-232 Concepts
The first part of this appendix, Introduction to RS-232 Communications,
introduces RS-232 communications concepts to users with no experience using
the RS-232 interface. The second part, Implementation of the RS-232 Interface,
describes implementation of the RS-232 interface on the 2714 or 2715 Spectrum
Analyzer. Other sections in this manual contain the detailed instructions needed
to operate over the RS-232. For example, Introduction to Programming, contains
the information needed to configure the 2714 or 2715 for most applications.
Programming includes an example of an interactive control program for the 2714
or 2715 Spectrum Analyzer. This program uses the RS-232 interface and a
Personal Computer (PC) controller. If additional RS-232 communications
information is needed, refer to the documents listed at the end of this appendix.
Introduction To RS-232 Communications
RS-232 communications follow a set of electrical, mechanical, and protocol
standards that are similar to the more familiar IEEE 488.1 GPIB standards.
Many types of devices are designed to communicate according to specifications
contained in standard EIA Std RS-232-C.
The RS-232 interface is NOT a bus (GPIB is a bus). Therefore, only one device
can be connected at a time. RS-232 uses an asynchronous serial data flow instead
of 8-bit parallel with byte-by-byte handshaking. RS-232 does not support device
addresses or serial polling.
The DCE (controller) and the DTE (terminal) must be configured the same way
for communications to occur successfully. To meet this requirement, commu-
nications parameters for the controller and terminal must be set independently.
Figure A–1 is a symbolic representation of how a character of data can be
transmitted over an RS-232 interface. It shows the encoding of the 7-bit, serial
character as it goes out the interface.
Data Bits
0
1
2
3
4
5
6
Start
Bit
Stop
Bit
Figure A–1: RS-232 Representation of a Character
RS-232 Signal
Components
Summary of Contents for 2714
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