ST10F276Z5 datasheet(231/239 Pages) STMICROELECTRONICS

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ST10F276Z5

Known limitations

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24.1.2

Concurrent transmission requests in DAR-mode (C-CAN module)

Description

When the C-CAN module is configured to operate in DAR mode (Disable Automatic

Retransmission) and the host requests the transmission of several messages at the same

time, only two of these messages are transmitted. For all other message transmission

requests the TxRqst bits are reset, no transmission is started, and NewDat and IntPnd are

kept unchanged. For the two messages which are transmitted, the TxRqst and NewDat bits

are reset and IntPnd is set if if it has been enabled by TxIE. TxRqst, NewDat and IntPnd are

bits of the message interface control registers.

The normal operation mode (DAR = 0) is not affected by this phenomenon.

Workaround

The DAR mode is intended to support time-triggered operation (TTCAN level 1) supporting

the transmission of a message only in its dedicated time window. It is an error to request the

transmission of several messages at the same time, and no workarounds should

consequently be necessary for TTCAN applications.

The progress of a requested transmission can be monitored by checking the message

object TxRqst and NewDat [optionally IntPnd] bits. In DAR mode, when a message

transmission has failed either because the transmission was disturbed or because it has not

started, it is necessary to request the message transmission again.

For details on DAR mode and message control registers, refer to user manual UM0409.

24.1.3

Disabling the transmission requests (C-CAN module)

Description

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

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

machine prepares the transmission, but before the transmission has actually started, then

this transmission request may remain disabled. It remains in this state even if the host

immediately re-enables it.

The status of the message object transmission request bit does not show that the

transmission is disabled. This only happens when the 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

corresponding to this message in the CPU interface register (Identifier, DLC, Data, with

TxRqst and NewDat [optionally TxIE] bits) and to transfer it into the message object. The

new content is then transmitted at the next opportunity, and is not altered by a possibly

ongoing transmission of the previous content of the same message object.

ST10F276Z5 Datasheet(PDF) 231 Page - STMicroelectronics

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