SM3000
Multipoint Videographic Recorder
7 Installation
116
IM/SM3000–EN Rev. L
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 selected in the instrument's
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.
Fig. 7.8 Two-wire and Four-wire Connection
Host Computer
+5V
0V
'A'
'B'
1.8k
W
Pull-down
Resistor
1.8k
W
Pull-up
Resistor
0V
+5V
0V
'A'
'B'
1.8k
W
Pull-down Resistor
1.8k
W
Pull-up
Resistor
Rx+
Rx
Tx
Tx+
COM
Terminal Block G
16
17
18
19
20
B Four-wire Connection
+5V
0V
1.8k
W
Pull-up
Resistor
1.8k
W
Pull-down
Resistor
Host Computer
Rx
Rx+
Tx
Tx+
'A'
'A'
'B'
'B'
GND
16
17
18
19
20
Tx+/Rx+
Tx/Rx
COM
Terminal Block G
A Two-wire Connection
See
Warnings