Termination Resistors; Rs485/422 Standard - ABB C1300 User Manual Supplement

C1300
Advanced Circular Chart Recorder

2.4 Termination Resistors

For long transmission lines, termination resistors are required on the last slave in the chain and the host computer/computer terminal
– see Fig. 2.3. Under normal operating conditions the resistors are required at the receive inputs only. For 2-wire operation the slave
termination resistor is fitted to the serial module terminal board – see Fig. 2.3A. For 4-wire operation the slave termination resistor is
selected using plug-in links on the serial module – see Fig. 2.3B.
2
3
4
5
6
A – 2-wire Operation
Note.

For 2-wire operation an external 120 resistor must be on the last slave in the chain. The resistor
is fitted across terminals 4 and 5 on the serial module terminal board.

For 4-wire operation the internal termination resistor on the last slave in the chain must be linked in.
Fig. 2.3 Slave Termination Resistors

2.5 RS485/422 Standard

The RS485 standard quotes connection of thirty two slaves maximum, to any single driver (computer terminal or host computer); the
RS422 standard quotes connection of up to ten slaves. However, these numbers can be increased if the driver's serial port permits.
IM/C1300–MOD Rev. C
Tx+/Rx+
120W
External Termination Resistor – see Notes
Tx–/Rx–
2 Electrical Installation
2 3 4
7 6
12 1
10 3 10
1 2
1
12 1
12
Termination Termination
Resistor Resistor
Linked In –
Linked Out
see Notes
B – 4-wire Operation
5 6
3
2
1
5