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18.7.3

Configuring a Transmit Object

Table 54 shows how a Transmit Object should be initialized.

The Arbitration Register values (ID28-0 and Xtd bit) are provided by the application. They

define the identifier and type of the outgoing message. If an 11-bit Identifier (“Standard

Frame”) is used, it is programmed to ID28 - ID18. The ID17 - ID0 can then be disregarded.

If the TxIE bit is set, the IntPnd bit will be set after a successful transmission of the Message

Object.

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 Register values (DLC3-0, Data0-7) are provided 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. The Dir bit should

not be masked.

18.7.4

Updating a Transmit Object

The CPU may update the data bytes of a Transmit Object any time through the IFn 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 IFn Data A Register or

IFn Data B Register have to be valid before the contents of that register are transferred to the

Message Object. Either the CPU has to write all four bytes into the IFn Data Register or the

Message Object is transferred to the IFn 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 Section

18.7.2.2: Message Transmission on page 242.

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

transmission has started.

Table 54. Initialization of a Transmit Object

appl.

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