L99LDLH32 datasheet(45/142 Pages) STMICROELECTRONICS

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DS12879 Rev 6

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L99LDLH32

Communication interface

141

The Commander may expect an answer from the addressed Responder after having sent a

diagnosis request within a given time frame. If the answer is not received the

communication with the addressed Responder may have been lost.

Sender bus block

The Responders check the bus for permanent recessive or dominant states. Both states

indicate a bus block and the sender may not be able to transmit any messages

Frame errors

Each received frame is verified in regard to these features:



CRC: the correctness of the received CRC for each frame is checked.



CRC Delimiter: after the CRC, one recessive bit as CRC delimiter has to be received;



Bit Stuffing: The correct position of the stuff bits is checked

If at least one of these conditions is not met, the frame is discarded.

Each transmitted frame is checked for:



Permanent recessive errors: If transceiver transmitter changes to dominant state, but

CAN bus does not follow for four times, the transceiver transmitter is disabled



Permanent dominant errors: if the bus state is dominant for t > 700 µs a permanent

dominant error is detected. The transceiver transmitter is disabled.

Invalid messages are not resent.

Error recovery: upon reception of a valid unicast frame, the transceiver transmitter is

enabled again.

6.4

Data handling

6.4.1

Overview

As described in the Section 6.2: Protocol overview, two basic message types are used:

broadcast messages, addressed to several Responders without any Responder answer;

unicast messages, addressed to individual Responder followed by Responder answer.

A Responder corresponds to a 16 channels entity, therefore the L99LDLH32 is a two

Responder device and has two Responder IDs, Responder ID0 and Responder ID1. Only

Responder ID0 (corresponding to the 16 channels entity of CH0 - Ch15) is programmable,

Responder ID1 (corresponding to the 16 channels entity of Ch16 - Ch31) is automatically

forced to Responder ID0+1. The Responder ID is programmable with 9 bits while its 2 LSB

are reserved to distinguish between different Responders within the device and shall be

programmed to “00” (any different value is ignored). This means that physical devices on

the bus are distinguished by Responder ID bits [8:2] – for example 0, 4, 8, 12, 16 …

In case of “Unicast communication” (see Section 6.6), a Commander can access all device

registers either using CAN ID equal to Responder ID0 or Responder ID1, while the ID of

response is always equal to (Responder ID0 | 0x200). A specific protocol is embedded into

the data of the unicast frames in order to allow to specify register address and type of

operation (read/write/clear).

In case of “Broadcast communication” (see Section 6.5), a Commander can send CAN FD

frame with 64 data bytes to several Responders. Each broadcast data frame has a specific

Chain ID (bits 0-5 of CAN ID field, see Section 6.5.3) which allows to distinguish between 64

different groups of Responders. Each Responder assigned to this Chain ID group can pick

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