L99LDLH32 datasheet(40/142 Pages) STMICROELECTRONICS

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Communication interface

L99LDLH32

40/142

DS12879 Rev 6

Communication interface

6.1

CAN FD Light compatible network protocol

The L99LDLH32 features a serial CAN FD Light compatible interface, a robust Commander-

Responder communication bus, restricted to the lamp internal communication.

It uses the CAN FD physical interface - therefore differential bus wiring – and a protocol that

can be implemented by a CAN FD protocol controller. It guarantees a defined edge density

for synchronization and, for safety, CRC and error checking are provided.

The system overview is shown in Figure 13. The communication Commander is

implemented in the Rear LED ECU using the protocol controller in the µC and a CAN FD

transceiver. An additional transceiver (e.g. LIN, High-Speed CAN or other) may be used by

the ECU to communicate with other ECUs in the car. The communication Responders are

located in the LED satellites.

Figure 13. System overview

6.2

Protocol overview

6.2.1

Basic function

The CAN FD Light compatible network is a bus system on which all participants share the

same differential wires. Messages being sent by one participant are received by all others.

Its protocol uses a Commander-Responder scheme. The Commander is implemented in the

host ECU while the Responders are built in the LED drivers.



The Responders only answer upon request by the Commander, therefore no collision

resolving mechanisms are needed.



Two basic message types are used: broadcast messages and unicast messages.



A broadcast message is sent to the Responders and expects no answer from them. The

Responders on the bus pick the data relevant for them from the message.



A unicast message is addressed to a specific Responder that answers by sending the

requested data.



A specific unicast message can be sent in predefined intervals to serve a watchdog

triggering. The unicast message can expect an answer from the addressed Responder

within a given time frame. Both mechanisms can be used to implement an efficient

supervision scheme, which allows the detection of a disconnected or failed network

participant.

Rear Light / Bus Commander

DCDC

Rear Light Satellite

L99LDLH32

...

Body Control Module

Communication

(LIN, CAN…)

Power Supply

CAN FD Light compatible

PHY

MCU

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