Group
Jumper connection Description
Notes
X7
1-2
B- bias enabled
COM1
2-wire connection
2-3
B- bias disabled
X8
1-2
A+ bias enabled
2-3
A+ bias disabled
X9
1-2
Bus termination ena-
bled
2-3
Bus termination disa-
bled
The bus is to be biased at one end to ensure fail-safe operation, which can be done
using the pull-up and pull-down resistors on the communication module. In 4-wire
connection the pull-up and pull-down resistors are selected by setting jumpers
X4, X5, X7 and X8 to enabled position. The bus termination is selected by setting
jumpers X6 and X9 to enabled position.
The jumpers have been set to no termination and no biasing as default.
Table 1070: 4-wire EIA-485 jumper connectors for COM2
Group
Jumper connection Description
Notes
X4
1-2
A+ bias enabled
COM2
4-wire TX channel
2-3
A+ bias disabled
X5
1-2
B- bias enabled
2-3
B- bias disabled
1
X6
1-2
Bus termination ena-
bled
2-3
Bus termination disa-
bled
1
X7
1-2
B- bias enabled
COM2
4-wire RX channel
2-3
B- bias disabled
1
X8
1-2
A+ bias enabled
2-3
A+ bias disabled
1
X9
1-2
Bus termination ena-
bled
2-3
Bus termination disa-
bled
1
It is recommended to enable biasing only at one end of the bus.
It is recommended to enable termination at each end of the bus.
It is recommended to ground the signal directly to earth from one node
using a GND pin and through capacitor from other nodes using a GNDC
pin.
1
Default setting
IED physical connections
1MRS757644 H
1182
620 series
Technical Manual
