Chassis Plans ATXP-875P, Technical Reference

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ATXP-875P Technical Reference Appendix C: Communication Devices
Chassis Plans 73
Advantages of Single-Ended Transmission
The advantages of single-ended transmission are simplicity and low cost of implementation. A single-ended system
requires only one line per signal. It is therefore ideal for cabling, and connector costs are more important than the
data transfer rate, e.g. PC, parallel printer port or serial communication with many handshaking lines, e.g. EIA-232.
Cabling costs can be kept to a minimum with short distance communication, depending on data throughput,
requiring no more than a low cost ribbon cable. For longer distances and/or noisy environments, shielding and
additional ground lines are essential. Twisted pair cables are recommended for line lengths of more than 1 meter.
TIA/EIA-422
TIA/EIA-422 (RS-422) allows a multi-drop interconnection of one driver, transmitting unidirectionally to up to 10
receivers. Although it is not capable of bidirectional transfer, it is still applicable and used for talker-audience
scenarios.
Electrical
TIA/EIA-422 (ITU-T V.11) is comparable to TIA/EIA-485. It is limited to unidirectional data traffic and is
terminated only at the line-end opposite to the driver . The maximum line length is 1200m, the maximum data
rate is determined by the signal rise- and fall-times at the receiver’s side (requirement: <10% of bit duration).
TIA/EIA-422 allows up to ten receivers (input impedance of 4 k
Ω
attached to one driver. The maximum load is
limited to 80
Ω
. Although any TIA/EIA-485 transceiver can be used in a TIA/EIA-422 system, dedicated TIA/EIA-
422 circuits are not feasible for TIA/EIA-485, due to short circuit current limitations. The TIA/EIA-422 standard
requires only short circuit limitation to 150 mA to ground, while TIA/EIA-485 additionally has to limit short circuit
currents to 250 mA from the bus pins to –7 V and 12 V to address malfunctions in combination with ground shifts.
RS-422 is terminated only at the line-end opposite to the driver even if there is only one receiver.
Protocol
Not applicable/none specified.