Installation guide

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Fig. 3: Example of RS485 communication
In addition to the data bits, we have the start, parity and stop bits.
Generally, one or several start bits are transmitted to indicate the start of data transmission. Next, the data
bits themselves are transmitted. A parity bit can be included (used to detect errors in the reception of the
frame) and finally the stop bits are sent.
5.2.1 Two wire RS485
As explained above, two different balanced signals are sent using cables A and B; however the signal is not
a differential signal between A and B but two different signals referenced to the same point (signal ground).
Fig. 4 Transmission of the two data signals with the same reference
RS485 is considered a two wire communication when only the wires corresponding with the two signals A
and B are connected in the line and all units transmit and receive over the same two wires. Note that this ac-
tually requires three wires as it must include the signal ground (GND) to provide the reference/0V.
The reference point (also called GND/Signal ground) from which signals A and B are obtained must be
common for the entire RS485 trunk.