Reminder on Single Line Polarization in RS 485
(Original Document)
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General
Single line polarization is the polarization used for Modbus type networks.
General architecture diagram of a RS 485 network:
Connection of Network Units
The network is made up of one shielded twisted pair. The connection of the network's different units is carried out as follows:
Step
Instruction
1
Link all outputs labeled + (Tx+, Rx+) to the network wire labeled: L+.
2
Link all outputs labeled - (Tx-, Rx-) to the network wire labeled: L-
3
Adapt the impedance of the network to the average of the two adaptation elements (Rc) located on the two end stations of the network.
4
Connect the wire L+ to 5 V and the wire L- to 0.V via the two polarization resistors (Rp = 470 Ω) to achieve polarization of the network.
This polarization continuously circulates a current in the network.
Polarization can be anywhere on the network (in practice it is generally done at master level).
There must be single polarization for the entire network, whatever its range.
Integral Characteristics
Integral characteristics are: