RM0319 datasheet(202/368 Pages) STMICROELECTRONICS

202 / 368 page

Controller area network ports (CAN)

RM0319

202/368

Doc ID 022640 Rev 3

If the RmtEn bit is set, a matching received remote frame will cause the TxRqst bit to be set;

the remote frame will autonomously be answered by a data frame.

The Data registers (DLC3-0, Data0-7) are given by the application, TxRqst and RmtEn may

not be set before the data is valid.

The Mask registers (Msk28-0, UMask, MXtd and MDir bits) may be used (UMask=’1’) to

allow groups of remote frames with similar identifiers to set the TxRqst bit. For details, see

Receive/Transmit Priority. The Dir bit should not be masked.

15.4.10

Updating a transmit object

The CPU may update the data bytes of a Transmit Object any time via the IFx Interface

registers, neither MsgVal nor TxRqst have to be reset before the update.

Even if only a part of the data bytes are to be updated, all four bytes of the corresponding

IFx Data A register or IFx Data B register have to be valid before the content of that register

is transferred to the message object. Either the CPU has to write all four bytes into the IFx

Data register or the message object is transferred to the IFx Data register before the CPU

writes the new data bytes.

When only the (eight) data bytes are updated, first 0x0087 is written to the Command Mask

To prevent the reset of TxRqst at the end of a transmission that may already be in progress

while the data is updated, NewDat has to be set together with TxRqst. For details, see

Transmission of messages.

When NewDat is set together with TxRqst, NewDat will be reset as soon as the new

transmission has started.

15.4.11

Configuring a receive object

Table 60 shows how a transmit object should be initialized.

Table 60.

Initialization of a receive object

The Arbitration registers (ID28-0 and Xtd bit) are given by the application. They define the

identifier and type of accepted received messages. If an 11-bit Identifier (“Standard Frame”)

is used, it is programmed to ID28 - ID18. ID17 - ID0 can then be disregarded. When a Data

Frame with an 11-bit Identifier is received, ID17 - ID0 will be set to ‘0’.

If the RxIE bit is set, the IntPnd bit will be set when a received Data Frame is accepted and

stored in the message object.

The data length code (DLC3-0) is given by the application. When the message handler

stores a data frame in the message object, it will store the received data length code and

eight data bytes. If the data length code is less than 8, the remaining bytes of the message

object will be overwritten by non specified values.

MsgVal

Arb

Data

Mask

EoB

Dir

NewDat

MsgLst

RxIE

TxIE

IntPnd

RmtEn

TxRqst

appl.

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