APC 66123 installation manual Jbus/Modbus, Polarity, Termination, SA1 description

JBUS/MODBUS

RS232 link configuration and connection

5 4 3 2 1

SG Txd Rxd

Pin	Function
1	Received data (input)
2	Not connected
3	Transmitted data (output)
4	Not connected
5	Signal ground

SA2SA1

SA2

1

8

ON

OFF

RS485 link configuration and connection

For proper operation, the polarity of EIA RS485 2-wire and 4-wire lines must be set at only one point and the lines terminated at the end.

Polarity

Normally, the master of the network sets the polarity of the line. The receiver inputs have a true failsafe feature wich eliminates the need for external bias resistors and ensures a logic high output level when the inputs are open or shorted. This guarantees that the receiver outputs are in a known state before communication begins and when communication ceases.

Termination

Termination is used to match impedance of a node to the impedance of the transmission line being used. When impedance are mismatched, the transmitted signal is not completely absorbed by the load and a portion is reflected back into the transmission line. The termination line is not necessary if the speed on the line is much less than 115Kbauds

RS485

0 V

RD = (B')

RD = (A')

TD = (B)

TD = (A)

1 R-

2 R+

3 T-

4 T+

5 0 V

SA2

SA1

SA2SA1

1	1
8	8
OFF ON	OFF ON

The default setting of the RS485 is a 4 wires configuration without polarity and without termination.

SA1 switches are used to make the termination and the topology of the line (2 or 4 wires). The termination resistance value is 166 Ω.

SA1 description:

1 : reserved

2 : reserved

3 : link termination between T- to R- (2 wires configuration) if set to ON

4 : connection T- to R- (2 wires configuration ) if set to ON

5 : connection T+ to R+ (2 wires configuration ) if set to ON

6 : reserved

7 : reserved

8 : link termination between R+ and R- if set to ON

3402230800/AC - 9