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REF: CCU/IO-485.DOC REV: C June 20, 2000
Appendix A - Wiring for RS485 chain:
1
2
3
4
A
B
C
D
4
3
2
1
D
C
B
A
CCU-Net ( A data collection , transportation and control network)
Connecting CCU/IO cards to a CCU/485-IO
CCU/485-IO
Power
Supervisory
485 Chn A
485 Chn B
RS232 Serial Port
RXA+
RXA-
SCREEN A
IN
IN
1
2
3
1
2
3
Screw
Terminals
RXB+
RXB-
SCREEN B
IN
IN
Screw
Terminals
Relay
Connection.
Connect to CCU-NET
Connector
Terminating Resistor
Terminating resistor
at CCU/485-IO
at Final CCU/IO.
Calculating the Value of the Terminating Resistor.
Terminating Resistor = 2 * transmission line impedance.
Example 1: for 50 Ohm individually screened pair data cable use 100 Ohm resistors.
Example 2: for 600 Ohm telephone communications cable use 1200 Ohm resistors.
Note 1: RS485 is designed to use 50 Ohm twisted pair.
Cabling recommendations.
1. Do not run the RS485 within telephone cabling
as this will violate safety of the telephony network.
RS485 power levels and harmonics are far greater
than the minimal level required to prevent cross
induction between audio channels.
RS485 will produce an annoying data stream buzz
on audio channels and subsequent complaints.
2. The greatest transmission length can be achieved
with twisted pair , low capacitance , screened
data grade 50 Ohm cable.
By using good quality cable and avoiding sources of
noise such as transmitters and mains cables a distance
of around 50 metres is possible. Each node added to
3. Before working on the cable check the DC and
AC voltage levels with a suitable multimeter.
This may save your life in the event that the data
cable has inadvertently become connected to a
source of power.
the network reduces the overall cable length.
485-
COM
485+
RS232-A
CCU/I or CCU/IO
IN1
IN2
IN3
IN4
IN5
IN6
IN7
IN8
DCE
485-
COM
485+
RS232-A
CCU/I or CCU/IO
IN1
IN2
IN3
IN4
IN5
IN6
IN7
IN8
