LDLL16ENTR datasheet(34/102 Pages) STMICROELECTRONICS

34 / 102 page

The data field can be up to 64 bytes long, the number of bytes is encoded in the data length code (DLC) field.

Depending on the number of data bytes either CRC17 or CRC21 is calculated. Only one CRC delimiter bit is sent

and accepted since the data bit rate is the same as the arbitration bit rate.

The arbitration and data bit rate are both 1 Mb/s. The bit rate is not switched.

5.4.2

Wake up

The responders support a power down mode out of which they can be woken up by the wake-up frame shown in

the Table 10.

5.4.3

Error frames

No error frames are sent by the responders. Error frames may be sent by the commander but are ignored by the

responders.

5.4.4

Collisions

Since the communication is always controlled and initiated by the commander, the bus participants do not

arbitrate. Collisions lead to data frame errors.

5.4.5

Error handling

Network participant disconnect

Since all participants share the same bus, various mechanisms allow the detection of a disconnected device.

After each sent frame at least one acknowledge is expected from a receiver. If this acknowledge is not received it

can be assumed that the sender is not connected to the network.

Broadcast frames can be transmitted within a given interval. Responders not receiving a broadcast frame after a

defined time may have lost their connection to the commander.

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

The checks permanent dominant and permanent recessive are made by the external transceiver.

Invalid messages are not resent.

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

5.5

Data handling

5.5.1

Overview

As described in the Section 5.3: Protocol overview, two basic message types are used: broadcast messages,

addressed to all responders without any responder answer; unicast messages, addressed to an individual

responder followed by responder feedback. The responder ID is 9 bits wide.

LDLL16EN

Communication interface

DS14111 - Rev 5

page 34/102

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