GE OPTIMA MR360 Service Training page 92

CAN stands for Controller Area Network, which is a vehicle bus standard designed to allow
microcontrollers and devices to communicate with each other within a vehicle without a
host computer. It is also used in other areas such as industrial automation and medical
equipment. Since MGD was introduced into GE MR system, CAN replaces the MDS link
gradually. In different systems, the components connected through CAN link are different.
1. SCP3 is in charge of receiving and managing the system data, sending control instructions
and monitoring the status of all connected node devices through the CAN link.
2. Every node device has its own built-in CAN communication controller. All controllers are
powered by a single isolated +24V power supply in the cabinet monitor.
3. CAN needs terminator resistor to balance the impendence of the network. One 120ohms
resistor is embedded in the SCP3 board, and another 120ohms resistor is installed on the
farthest node - Cabinet Monitor.
4. The DC24V ISO power is provided by Driver Module in HD, HDx system. In Emergency Off
mode, Driver Module will lose power and the CAN link is broken. The system requires a TPS
reset after power restoration. In SV system however, CAN 24V DC power is supplied by
Cabinet Monitor, and it is still energized when system is in Emergency Off mode, so TPS reset
is unnecessary after power is restored.
5. In service browser, CAN diagnostic tool can be used to check if the CAN link works
normally. Cabinet Monitor should be always connected because it supplies the 24V DC
power for the whole CAN link. We can bypass one node by removing the CAN in and out
cables and directly connecting the two cables except the driver module lite, because the
CAN cables connectors in driver module are both male.
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