ST10F280 datasheet(125/186 Pages) STMICROELECTRONICS

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ST10F280

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Message Control Register (EFn0h/EEn0h)

XReg

Reset Value: UUUUh

Notes 1. In message object 15 (last message) these bits are hardwired to “0” (inactive) in order to prevent transmission of message 15.

2. When the CAN controller writes new data into the message object, unused message bytes will be overwritten by non specified

values. Usually the CPU will clear this bit before working on the data, and verify that the bit is still cleared once it has finished working

to ensure that it has worked on a consistent set of data and not part of an old message and part of the new message.

For transmit-objects the CPU will set this bit along with clearing bit CPUUPD. This will ensure that, if the message is actually being

transmitted during the time the message was being updated by the CPU, the CAN controller will not reset bit TXRQ. In this way bit

TXRQ is only reset once the actual data has been transferred.

3. When the CPU requests the transmission of a receive-object, a remote frame will be sent instead of a data frame to request a

remote node to send the corresponding data frame. This bit will be cleared by the CAN controller along with bit RMTPND when the

message has been successfully transmitted, if bit NEWDAT has not been set. If there are several valid message objects with pending

transmission request, the message with the lowest message number is transmitted first.

9876543210

RMTPND

TXRQ

MSGLST

CPUUPD

NEWDAT

MSGVAL

TXIE

RXIE

INTPND

Bit

Function

INTPND

Interrupt Pending

Indicates, if this message object has generated an interrupt request (see TXIE and RXIE), since

this bit was last reset by the CPU, or not.

RXIE

Receive Interrupt Enable

Defines, if bit INTPND is set after successful reception of a frame.

TXIE

Transmit Interrupt Enable

Defines, if bit INTPND is set after successful transmission of a frame. 1

MSGVAL

Message Valid

Indicates, if the corresponding message object is valid or not. The CAN controller only operates on

valid objects. Message objects can be tagged invalid, while they are changed, or if they are not

used at all.

NEWDAT

New Data

Indicates, if new data has been written into the data portion of this message object by CPU

(transmit-objects) or CAN controller (receive-objects) since this bit was last reset, or not. 2

MSGLST

(Receive)

Message Lost (This bit applies to

receive-objects only)

Indicates that the CAN controller has stored a new message into this object, while NEWDAT was

still set, i.e. the previously stored message is lost.

CPUUPD

(Transmit)

CPU Update (This bit applies to

transmit-objects only)

Indicates that the corresponding message object may not be transmitted now. The CPU sets this

bit in order to inhibit the transmission of a message that is currently updated, or to control the

automatic response to remote requests.

TXRQ

Transmit Request

Indicates that the transmission of this message object is requested by the CPU or via a remote

frame and is not yet done. TXRQ can be disabled by CPUUPD. 1 3

RMTPND

Remote Pending (Used for transmit-objects)

Indicates that the transmission of this message object has been requested by a remote node, but

the data has not yet been transmitted. When RMTPND is set, the CAN controller also sets TXRQ.

RMTPND and TXRQ are cleared, when the message object has been successfully transmitted.

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