Two-Wire And Four-Wire Connection - ABB ControlMaster CM10 Communications Supplement

ControlMaster CM10, CM15, CM30 and CM50
Universal process controllers and indicators,

5.3 Two-wire and Four-wire Connection

MODBUS serial communications can be configured as either 2-wire or 4-wire serial links – see Fig. 5.1. The instrument must
be added to the link configuration on the host system – refer to information supplied with the host system.
Host Computer
'B'
'A'
+5 V
Tx+

1.8 k Pull-up
Tx–
Resistor
Rx+
'A'
Rx–
'B'

1.8 Pull-
down Resistor
GND
0 V
2-Wire Connection
Fig. 5.1 2-Wire and 4-Wire MODBUS Serial Links
IM/CM/C–EN
1 1
/ , /
8
Tx+/Rx+
Tx–/Rx–
COM
Standard Connections
1
and / DIN
4 2
Host Computer
+5 V

1.8 k Pull-up
0 V
Resistor
'B'
'A'

1.8 k
+5 V
Pull-down Resistor
1.8 k
0 V
Pull-up
Resistor
'B'
'A'

1.8 k
Pull-down Resistor
0 V
4-Wire Connection
5 MODBUS Communications
Tx+
Tx–

Rx+
Rx–
COM
Standard Connections
15