EP OS MOTOR MANAGEMENT SY STEM – INSTRUCTION MANUAL
4.5
CHAPTER 4: COMMUNICATION
4.1.4 Modbus topology
Figure 4-2 illustrates the standard two-wire Modbus topology. To minimize the effects of reflections from the ends of the RS-
485 cable caused by impedance discontinuities in the system, a line-terminating resistor on the RC network must be placed
near each end of the bus, as illustrated in Figure 4-2.
If one or more devices require polarization, one pair of resistors must be attached to the RS-485 balanced wire pair, as follows:
Pull-up resistor to 5 V on the positive line
Pull-down resistor to common on the negative line
These resistors must be between 450 and 650
Ω
. The latter may allow a higher number of devices to be connected to the
serial bus.
NOTE:
Pull-up and pull-down resistors are recommended in an industrial environment .
HOST (PCL/PC)
M
M C
o
o o
d
d m
b
b m
u
u o
s
s n
5V+ Common
–
+
TERMINATING RESISTOR
OR RC NETWORK
Common
TERMINATING RESISTOR
OR RC NETWORK
PE
PE
EntelliPro ES N
EntelliPro ES N
PE
PE
Figure 4-2: Two-wire Modbus topology.
