Interprocessor Communication (IPC)
62 RTHC-SVD01B-EN
12-3 c. Internal module failure:
Internal module failures usually result only in communication loss to
the failed module, but could, in some cases, affect all the modules
because the failed module may lock-up the IPC bus and prevent some
communications. The former can be identified by analyzing all of the
active diagnostics. The latter can be identified through a process of
elimination, whereby each module, in turn, is taken out of the IPC link
and a jumper is installed in its place. Reset the diagnostices and ana-
lyze the new diagnostics produced.
12-3 d. Incorrect Polarity:
Refer to the wiring schematic and confirm that all black wires in the
twisted pair connect to the positive (+) terminals (either pin 1 or 3) of all
the modules. Then confirm that all of the white wires of the twisted pair
connect to the negative (-) terminals (either pin 2 or 4) of all the mod-
ules.
12-3 e. High levels of Electro-Magnetic Interference:
The modules and the IPC link have been qualified under numerous
and severe EMI (both radiated and conducted) and the system judged
to be immune to all but extremely high noise levels. Always be sure to
close and latch the control panel cabinet doors as the panel enclosure
provides significant shielding and is integral in the overall noise immu-
nity of the control system.
12-3 f. Module specific function selected without the
Options Module:
If any of the functions on the Options module are selected but the
Options Module is not present, UCP2 will look for this module and gen-
erate an error. The Options module functions include Chilled Water
Reset, Ice Machine Control, External Chilled Water Setpoint, External
Current Limit Setpoint, and Tracer/Summit Communications.
12-3 g. Loss of common ground:
Verify that a good ground exists between all modules. The CLD
requires a dedicated green wire ground. Verify that it is in place and
has a good connection.
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