Specifications

Appendix C - Glossary of Terms RS-422 And RS-485 Applications Ebook
Page 127 of 137 Manual Documentation Number: <DocNumber>
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state. In the high impedance state the output is effectively open circuit and
does not apply either logic state, allowing other outputs connected to the same
output lines to share the media.
TVS (Transient Voltage Suppressor)
A device that suppresses voltages by conducting either positive or negative
voltages above the threshold voltage from one terminal to the other.
Electrically, a TVS works like back-to-back Zener diodes.
Twisted Pair Cable
A cable for serial communication which includes at least one twisted pair of two
wires. May be shielded or may provide a separate ground wire. Twists in the
wire provide noise cancelation as noise is induced on the lines in series
opposing causing it to cancel out.
Two-wire (RS-485)
A half duplex RS-485 connection system which uses one twisted pair for Data
A(-) and Data B(+), plus Signal Ground/Common.
Transmit and receive operations are on the same pair of wires, allowing all
devices on the bus to communicate with each other. The system requires that
each slave have a turn-around delay of one or more characters between
receiving data and responding. Each device must be separately addressable,
and ignore data/commands that do not apply to the device’s address. All Two-
wire RS-485 devices are normally in receive mode except when transmitting.
Receivers can either be disabled or enabled when the device is transmitting.
Disabling the receiver prevents an echo of the sent characters from being
received on the sending device (Echo off). Alternately, the sending device may
leave its receiver enabled to detect any collisions from other devices on the
bus (Echo on). Driver/Receiver control can either be implemented through
software in the node or through hardware. B&B converters and serial cards
offer this option through either the RS-232 RTS line for software control or
Automatic Send Data (SD) control in hardware.