INTRODUCTION TO SERIAL RELAY COMMUNICATIONS Caitlin Martin, BPA Hands On Relay School 2013
2
Serial Communications Outline 1. Serial Communication Overview 2. What is a Standard? 3. What is a Protocol? 4. RS-232 5. Cables 6. Flow Control 7. Terminal Emulator 8. Breakout Boxes 9. Converters 10. Review
What are Serial Communications? • Serial communication is the
process of sending data serially, one bit at a time. • Used for long distances. • Synchronization isn’t as important.
• Parallel communication sends
two or more data bits at a time over separate channels/pins.
6
WHAT IS A STANDARD?
7
What is a Standard? • A standard is “something considered by an
authority or by general consent as a basis of comparison; an approved model.” (Dictionary.com) • But, when you are talking about communications
a standard is a set of rules that determine the operating characteristics of the physical transport. • The standards are developed by authorities like
Electronic Industries Association (EIA), IEEE, or IEC. • Each standard defines certain characteristics that make it unique: voltage levels, signal timing, signal function, and mechanical connectors. • Standards can also be written to specify protocols.
How do they compare? Specs
RS-232 (1969)
RS-422 (older)
RS-485
Standard USB 2.0
Cabling
single ended
single ended multi-drop
multi-drop
Can be multi-drop with hub, but typically single ended
Number of Devices
1 transmit, 1 receive
5 transmitters, 10 receivers
32 transmitters or 32 receivers
127 including hubs
Communication Mode
Full duplex
Full duplex, half duplex
Full duplex (Tx+,Tx,Rx+,Rx-), half duplex (ATx-/Rx-, B- Tx+/Rx+)
