Rs422/485 Serial Communications; Host Computer Serial Communications; Two-Wire And Four-Wire Connection - ABB SM3000 User Manual

SM3000
Multipoint Videographic Recorder

7.5 RS422/485 Serial Communications

This section describes the connection of serial data cables
between the master (host computer) and slave instrument on a
Modbus serial link.

7.5.1 Host Computer Serial Communications

The optional serial interface module has been designed to
operate using the Modbus Remote Terminal Unit (RTU)
Master/Slave protocol.
An appropriate RS422/485 communications driver must fitted to
the host (Master) computer. It is strongly recommended that the
interface has galvanic isolation to protect the computer from
lightning damage and to increase signal immunity to noise
pick-up.

7.5.2 Two-wire and Four-wire Connection

Modbus serial communications must be configured as either
two-wire or four-wire serial links – see Fig. 7.8. Two-/four-wire
operation must also be
Configuration Level – see Section 6.7.4, page 105.
The instrument must be added to the link configuration on the
host system – refer to information supplied with the host
system.
116
selected in the instrument's
Terminal Block G
16
17
Tx+/Rx+
18
Tx–/Rx–
19
COM
20
A – Two-wire Connection
Terminal Block G
Tx+
16
Tx–
17
Rx+
18
Rx–
19
COM
20
B – Four-wire Connection
See Warnings on Page 112
Fig. 7.8 Two-wire and Four-wire Connection
7 Installation
Host Computer
'B'
'A'
+5V
Tx+
1.8kW Pull-up
Tx–
Resistor
Rx+
'A'
Rx–
'B'
1.8kW Pull-down
Resistor
GND
0V
Host Computer
+5V
1.8kW Pull-up
0V
Resistor
'B'
'A'
1.8kW
Pull-down
+5V
Resistor
1.8kW
0V
Pull-up
Resistor 'B'
'A'
1.8kW
Pull-down Resistor
0V
IM/SM3000–EN Rev. L