CCS Smart Equipment Control Board for Single Packaged Unit (SPU) Controller Installation Instructions
5
End-of-Line (EOL) Terminations
Daisy-chained RS485 protocol networks require
end-of-line (EOL) termination to reduce interference.
Interference is caused by signal reflection that occurs
when data transmissions reach the end of a bus
segment and bounce back (Figure 5). The high baud
rates on Master-Slave/Token-Passing (MS/TP) bus
applications require robust EOL termination and strict
adherence to the EOL termination rules.
On a CCS System bus or Zone bus, only one EOL
termination is required due to the fewer number of
devices on one bus and the shorter wiring length.
Specifically, the System bus must always have a
System Manager as the EOL device, and the Zone bus
must always have a Zone Coordinator as the EOL
device. Figure 6 shows a CCS EOL wiring example.
No EOL = No Signal Cushioning
(Bounce Back and Noise)
No
EOL
EOL
EOL Provides Signal
Cushioning (No Bounce Back)
FI
G
:in
tr
fr
n
c
Figure 5: Interference
Figure 6: CCS EOL Wiring Example
Input
Output
Module
24V
COM
COM
-
+
BI-1
COM
BI-2
COM
AI-3
COM
AI-4
Monitored Contact
To Temperature,
RH%, CO
2
Sensor,
Building Pressure,
Light Sensor,
Refrigerant Sensor,
Common Flow
To 24VAC
BO-3
BO-2
BO-1
BO-4
COM
Monitored Contact
To Scheduled Item 1
To Scheduled Item 2
To Scheduled Item 3
To Scheduled Item 4
Non-
CCS
HVAC
System
Universal
CV Unit
Controller
24V
COM
Zone Sensor
COM
-
+
AI-1
COM
AI-2
1
2
3
4
BO-1
BO-2
BO-3
BO-4
BO-5
C
R
G
Y1
Y2
W1
W2
COM
AI-6
COM
AI-7
COM
AI-8
COM
AI-4
COM
AI-5
COM
BI-2
SAT Sensor
RAT Sensor
OAT Sensor
To Zone RH% Sensor
To Zone CO
2
Sensor
APS
COBP Zone Coordinator
System
Bus
COM
SB
-
SB
+
EOL
O
N
?
Zone
Bus
COM
ZB
-
ZB
+
EOL
O
N
?
COM
24V
LAN
To 24VAC
System Manager
System
Bus
COM
SB-
SB+
EOL
O
N
?
Zone
Bus
COM
ZB
-
ZB
+
EOL
O
N
?
COM
24V
Modem
LAN
To 24VAC
To Phone Line
To Ethernet Hub
VAV Zone Coordinator
System
Bus
COM
SB-
SB+
EOL
O
N
?
Zone
Bus
COM
ZB
-
ZB
+
EOL
O
N
?
COM
24V
LAN
To 24VAC
tape
off
SEC Unit Control Board
COM
-
+
This end of the Drain Wire
connected to cabinet ground
Other System Bus Devices
CCS System Bus Devices
Other System Bus Devices
Other System Bus Devices
To COBP Zone
Bus Devices
To VAV Zone
Bus Devices
Recommended ZC end-of-line for zone bus
Recommended SM end-of-line for system bus
Must be end of line for zone bus
TEC2601-4
TEC2602-4
TEC2603-4
Y2
Y1
G
RC
C
RH
W1
W2
Aux
DI1
DI2
RS
Scom
OS
MS
+
_
Ref
CO
M
-
+
