Watson-Marlow MM420 - Manual (Page 119)

Issue 10/06 3 Functions
MICROMASTER 420 Operating Instructions
6SE6400-5AA00-0BP0 119
When the MICROMASTER is used in an RS485 bus communications network the
following is required:
1. A power supply
2. A terminating resistor between P+ and N- at both bus ends
(refer to Fig. 3-41)
Control terminals
RS485 terminator
14
P+
15
N-
1
+10 V
2
0 V
to terminal 2 of the next slave
Fig. 3-41 Connecting the RS485 terminator
If the frequency inverter is the last slave on the bus (refer to Fig. 3-40), then the P+
and N- of the RS485 terminator provided must be connected there to the RS485
terminals (refer to Fig. 3-41). P10 and 0 V can be connected to terminals 1 and 2
for the power supply.
If the first or last node is not a MICROMASTER 4 the bus should be terminated
between P+ and N- with a resistor (with a value between 120
Ω and 220 Ω ).
The bus must be biassed (pull-up resistor from P+ to P5 or P10, pull-down from N-
to 0 V) at one or both ends. If the first and/or the last node is not a
MICROMASTER 4 (e.g. a S7-200 series PLC), the bus can be biassed by
connecting a 390 Ω
resistor from P+ to P5 and a 390 Ω pull-down resistor from N-
to 0 V.
SIMATIC PROFIBUS connectors, e.g. 6ES7972-0BA41-0XA0, can be used for
biassing and termination when the first or last node is an S7-200 series PLC.