Selco
C6200 FlexGen
Revision: 03-06-2014
Page 22 of 24
5.13 RS485
The C6200 FlexGen module includes an isolated RS485 interface.
Terminal
Description
Signal
Connection
Left
A -
RS485 A
B signal of the RS485 bus
Middle
B +
RS485 B
A signal of the RS485 bus
Right
REF
Reference (isolated)
Reference of the RS485 bus
It is important to note that the RS485 reference is isolated from the common COM of the module.
The 3-wire RS485 bus is connected from module to module.
A RS485 bus needs termination resistance (150
Ω)
between terminals A and B at end end of the
cable. It is not necessary to connect external termination resistors as the C6200 FlexGen contains
internal resistors that can be enabled by toggeling DIP switch 5 to ON position. The termination
resistor must be enabled only on the first and on the last unit on the RS485 bus.
The maximum cable length for RS485 is 1.000 meters. The cable must be twisted pair (A and B
twisted inside the cable). The cable should be shielded. One end of the shield (and only one end)
nust be connected to switchboard chassis.
C
ri ab
T
Cable
K
B
8
1
P
1
E-DEXN/
B
T
can be used
It is sometimes necessary to fix the potential of the RS485 + and
–
lines due to interference from
other sources. This is done with two 1 k
Ω
resistors using
a technique called “Biasing”
. One resistor
is fixed between RS485 B and an ex5 V DC supply, the other is fixed between RS485 A and
the reference of the -5 V DC supply. The reference of the 24 VDC (terminal 32) supply must then
be connected to rightmost terminal of the RS485 plug on each and every module.
PLC
Set
7
Dip-switch