Electrical Installation; Selection Of Serial Communication Adaptors For Personal Computers; Recommended Opto22 Boards; Pull-Up And Pull-Down Resistors - ABB C1900 Installation Manual

2 ELECTRICAL INSTALLATION

2.1 Selection of Serial Communication Adaptors for Personal Computers

Information.
• A RS422/485 communication board is required in the host PC.
• Observe the limitations outlined in the Installation Guide – the maximum serial data transmission line length for both
RS422 and RS485 systems is 1200m.
An RS422/485 communications adaptor is required for serial links. It is strongly recommended that the card used has galvanic
isolation to protect the computer from lightning damage and increase immunity from noise pick-up.

2.2 Recommended OPTO22 Boards

The following OPTO22 boards are recommended for use with the COMMANDER 1900 Series of instruments:
Part No. Computer Type
AC24 AT AT Bus IBM PC compatible
AC34 Microchannel IBM PC
2.3 Pull-up and Pull-down Resistors – Figs. 2.1 and 2.2
To prevent false triggering of the slave (COMMANDER 1900) by the presence of noise when the master (host computer) is
inactive, 1.8K pull-up and pull-down resistors must be fitted to the RS422/485 adaptor card – see Figs. 2.1 and 2.2.
COMMANDER 1900

Pull-up and Pull-down Resistors

'B'
1.8kΩ Pull-up
Resistor
'A'
+5V
'B'
'A'
1.8kΩ Pull-down
Linked In Linked Out
6
7
8 5
9
10
Links on Serial Module
2
Serial Module
Terminal Board
1
Tx–/Rx–
2
Tx+/Rx+
3
4
5
6
7
0V
8
Resistor
9
4
3
Note. If an RS422/485 adaptor card without pull-up and pull-down
resistors is used, the COMMANDER 1900's internal resistors can be
linked in.
Fig. 2.1 Pull-up and Pull-down Resistors (3-wire Operation)
Computer Terminal or Host Computer
Tx+
Tx–
Tx+
Rx+
Rx–
Tx–
GND
GND
'B'
'A'
+5V +5V
1.8kΩ Pull-up Resistor
'B'
'A'
1.8kΩ Pull-down Resistor
0V