ST10F272Z2_08 datasheet(132/189 Pages) STMICROELECTRONICS

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Known limitations

ST10F272Z2

132/189

24.3

Transmission request disabled (C-CAN module)

Description

The transmission request of a message object may remain disabled (even if the host

immediately enables it again) in the following situations:

if the host disables the pending transmission request of the lowest-priority message

object (number 32 by default) in the short time window during which the message

handler state machine prepares the transmission of the message

if the transmission has not started.

Reading the transmission request bit of this message object does not show that the

transmission request is disabled. This only happens when this message object is the only

one with a pending transmission request.

If the transmission request is blocked in the disabled state, it will be re-enabled by the first

activity detected on the CAN bus or by setting the transmission request of any other

message object.

The other message objects are not affected by this phenomenon.

Workaround

It is usually not necessary to disable the transmission request of a message object. If the

message object is to be used for another message, it is sufficient to prepare the new content

for this message object in the CPU interface register (Identifier, DLC, Data, with TxRqst and

NewDat [optionally TxIE] bits) and to transfer this content into the message object. The new

content is transmitted at the next opportunity. It is not altered by a possibly ongoing

transmission of the previous content of the same message object.

ST10F272Z2 数据表(PDF) 132 Page - STMicroelectronics