Multiplexing; Multiplexing And The Canbus; Troubleshooting The Canbus - Yale 524150797 Maintenance Manual

ELECTRICAL SYSTEM

MULTIPLEXING AND THE CANBUS

Controller Area Network (CAN) Bus communication
allows multiple modules to communicate with each
other using the same digital data on a shared net-
work, this method of communication is known as mul-
tiplexing. The CANbus is a pair of twisted insulated
wires that interconnect all the modules on the net-
work. The data transmitted is a digital encoded for-
mat. Digital means only two states are used to trans-
mit data, High/On and Low/Off. This eliminates the
need for each module to be hard wired to each sen-
sor. Using Multiplexing, sensor information that may
be received by one module, can then be shared with
all other modules. The information is sent out over the
CANbus in an encoded form and any other module
that requires the information can pick it out from the
data stream.
The CANbus has two termination resistors (120
ohms) that are connected in parallel. When resistance
checks are performed, a normal operating system will
display 60 ohms between the CAN LO and CAN HI
circuits.
The first 120 ohm termination resistor is located inside
the Tiller Control Card. To diagnose, proceed to Trou-
bleshooting the Tiller Control Card Termination Resis-
tor.
The second 120 ohm termination resistor is located in
the Traction Controller. To diagnose, proceed to Trou-
bleshooting the Traction Controller Termination Resis-
tor.

Troubleshooting the CANbus

NOTE: Refer to the latest Diagram YRM for the most
current circuit information.
When the CANbus is active and modules are commu-
nicating, CAN HI and CAN LO voltage will be approxi-
mately 5 volts when added together. If both CAN HI
and CAN LO have consistent 2.5 volt, there is no
communication on the CANbus.
Check the Service Manual section in Yale Axcess Online for possible updates and check pertinent Bulletins
General Maintenance and Diagnostic Data

Multiplexing

If CAN HI is shorted to B(-) or CAN LO is shorted to
battery voltage, network communication will stop.
If you measure battery voltage on the data link, there
is a short to power in the circuit.
If you measure 0 volts while the CANBus is active,
there is a short to B(-) or an open in the circuit.
Internal control module failures can stop the entire
network from communicating. If there are no harness
problems, disconnect control modules one at a time
until CANbus communication returns.
With both 120 ohm termination resistors connected to
the CANbus, resistance between the two circuits
should read 60 ohms.
If CANbus resistance is 120 ohms, there is an open
circuit or a termination resistor is missing.
If resistance is 0 ohms, the two circuits are shorted to-
gether.
1. Measure voltage between the diagnostic connec-
tor, socket A and B(-).
NOTE: Key in ON position.
Is voltage approximately 2.5 volts?
YES- Proceed to Step 2.
NO- Inspect CAN HI circuit for open or short; if volt-
age is 0 volts, the CAN HI circuit is shorted to B(-)
or open. If voltage is above 5 volts, the CAN HI is
shorted to power.
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