CCS Smart Equipment Control Board for Single Packaged Unit (SPU) Controller Installation Instructions
7
Correcting Physical Communication Bus Problems
The communication bus is subject to a number of
physical factors that can affect performance. Consider
the following list of common physical problems that
affect the communications bus:
•
Check wires
-
Verify that the wire is 22 AWG (0.65 mm) 3-
conductor, twisted, shielded cable.
-
Verify that the shield is continuous and hard-
grounded at one end.
•
Check wiring
-
Check for and eliminate T-Taps (wire
configurations that create a T shape) and star
configurations.
-
Ensure that the bus is wired in daisy-chain
fashion.
-
Verify that appropriate devices have three
wires entering and exiting each terminal.
(Devices at the ends of the trunk do not have
this wiring.)
•
Check EOL switch settings
-
Verify that the zone bus EOL switch on the
Zone Coordinator is set to ON and the Zone
Coordinator is located at the end of the zone
bus trunk.
-
Verify that only the EOL switch at the end of
the system bus is set to ON and all other
system bus EOL switches are set to OFF.
•
Check connections, polarity, and lengths
-
Verify that communications loops are less than
approximately 304 m (1,000 ft) total in length
-
If you are using one transformer to power
multiple devices, verify that the device 24 VAC
power connection follows the polarity of the
common and 24 V terminations (see
).
•
Check for opens and shorts
•
Check terminations
•
Check addresses
-
Check for duplicate addresses.
-
Verify that the address range is sequential.
•
Check for sources of interference
•
Check the status LED to verify power at the
controller.
•
Check bus voltages:
-
(+) to COM must be within 2.0 to 3.0 VDC
-
(-) to COM must be within 1.5 to 2.54 VDC
-
(+) to (-) must be within 0.3 to 1.0 VDC
Note:
Values may fluctuate due to ongoing
communications; this operation is normal provided
the voltage is within the defined range.
Repair Information
If the Unit Control Board (UCB) fails to operate within
its specifications, replace the unit. For a replacement
controller, contact the nearest Johnson Controls®
representative.
