Electrical Installation; Host Computer Serial Communications; Opto22 Boards For Use With Personal Computers; Two-Wire And Four-Wire Connection - ABB C250 User Manual

2 ELECTRICAL INSTALLATION

This section describes the connection of serial data transmission cables between the
master (host computer) and slave COMMANDER 250/V250 instruments on a
MODBUS serial link. All connections other than those used for serial communication
are shown in Section 5 of the relevant User Guide .

2.1 Host Computer Serial Communications

An RS422/485 communications driver must be fitted to the host computer. It is
strongly recommended that the interface has galvanic isolation to protect the
computer from lightning damage and increase signal immunity to noise pick-up.

2.2 OPTO22 Boards for use with Personal Computers

Where a personal computer is used as the host computer, the following OPTO22
boards are recommended for use with the COMMANDER 250/V250 Series of
instruments:
Part No. Computer Type
AC24 AT AT Bus IBM PC compatible
AC34 Microchannel IBM PC
2.3 Two-wire and Four-wire Connection – Figs. 2.1 and 2.2
MODBUS serial communications must be configured as either two-wire or four-wire
serial links – see Figs. 2.1 and 2.2. Two-/four-wire operation must also be selected in
the Configuration Mode – see Section 3.1.
C250
V250
32
33
34
35
36
Fig. 2.1 Pull-up and Pull-down Resistors (Two-wire Operation)
Host Computer
Tx+
Tx–
Tx+/Rx+
Rx+
Rx–
Tx–/Rx–
GND
GND
'B'
'A'
+5V
1.8kΩ Pull-up
Resistor
'A'
'B'
1.8kΩ Pull-down
Resistor
0V
Refer to
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