ControlMaster CM10, CM15, CM30, CM50, CMF160 and CMF310
Universal process controllers and indicator,
1
/8,
1
/4,
1
/2 DIN and fieldmount 5 MODBUS Communications
16 IM/CM/C–EN Rev. H
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. 5.2. The instrument must
be added to the link configuration on the host system – refer to information supplied with the host system.
Fig. 5.2 2-Wire and 4-Wire MODBUS Serial Links
'A'
'B'
'A'
'B'
Host Computer
Host Computer
2-Wire Connection
4-Wire Connection
'A'
'B'
'A'
'B'
Tx+/Rx+
Tx–/Rx–
COM
Tx+
Tx–
Rx+
Rx–
GND
0 V
1.8
Pull-down
1.8 k
Pull-up
Resistor
+5 V
Tx+
Tx–
Rx+
Rx–
COM
0 V
+5 V
0 V
+5 V
1.8 k
Pull-up
Resistor
1.8 k
Pull-down Resistor
1.8 k
Pull-up
Resistor
0 V
1.8 k
Pull-down Resistor
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