Specifications

Appendix C - Glossary of Terms RS-422 And RS-485 Applications Ebook
Page 100 of 137 Manual Documentation Number: <DocNumber>
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A
ASCII
American Standard Code for Information Interchange
Asynchronous
Form of serial communication used on personal computer RS-232 ports, RS-
485 and most RS-422 communications. No separate synchronizing clock signal
needs to be transmitted for the data. This non-synchronous serial
communications format uses standard preset baud rates based on a crystal
reference for transmit timing, and uses the received data Start Bit and a local
crystal reference to read the remaining bits near the center position. Compare
to synchronous transmission which requires two synchronizing signals, receive
clock and transmit clock plus two data signals.
Automatic Send Data Control
Circuitry found on many RS-485 products which senses the presence of RS-
485 data to be transmitted and sets the RS-485 transmitter line driver on to
send the data. At the end of transmission, it returns the line driver to a high
impedance (disconnected) state. Can also disable the receiver (for Echo Off)
during transmit, enable it again at the end of transmission.
B
Bad Node (RS-485)
A device or RS-485 driver/receiver unit which cannot be communicated with. A
bad node can be caused by defective wiring or a loss of power (when devices
are not tri-stated during power off), or by failure in one device that blocks the
data to all the others.