Functional description and allocation of terminal pins Manual BG41/BG42/BG43
3-14 Rev. 99/49
3.2.4 RS422/RS485 module (MD21)
3.2.4.1 General
The RS422 interface is suitable for transmission lengths of up to 1200m. In using a four-wire line,
data can be simultaneously sent and received. As a result of the symmetrical transmission a higher
interference immunity is achieved. Coupling on the grounding conductor does not influence the
signal. One advantage in comparison to the RS232C interface is its bus capabilities. It can be
connected to up to 16 suscribers.
The RS485 interface was developed, in order to enable a higher number of bus suscribers to be
connected to the bus operation. Up to 32 suscribors can in this case be connected. Similar to the
RS422, the transmission is symmetrically constructed, but here one has a higher interference
immunity. By using repeaters (signal amplifiers) the distance can be doubled.
The RS422/RS485 module serves the point-to-point or the multipoint connection on the basis of the
RS422/RS485 norm. A load resistance of 100Ω can additionally be connected. The module is non-
floating.
When using the RS422/RS485 module in its delivery state the jumper for the 100Ω resistance is
plugged into the OFF position.
Fig. 3-13: Structure of the RS422/RS485 module
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