The Message ID bits that are checked with the arbitration of the receiver buffer bits are
the corresponding bits on the Acceptance Mask only if set to 1.
This filtering function is implemented for every message buffer.
TX Message Buffer
The AT7908E CAN controller has one transmitter buffer. The transmitter buffer is com-
posed of 12 registers of 8 bits. The firsts 4 registers are used for the arbitration part that
could be of 11 or 29 bits. If the message to transmit is a standard message, the
AT7908E will send on the bus the identifier from ARB28 to ARB18. The other 8 registers
contain the data byte of the message:
TX_ARB0: bits 28 down to 21 of the arbitration of the transmitter
buffer(TXARB28:TXARB21)
TX_ARB1: bits 20 down to 13 of the arbitration of the transmitter
buffer(TXARB20:TXARB13)
TX_ARB2: bits 12 down to 5 of the arbitration of the transmitter buffer (TXARB12:TXARB5)
TX_ARB3: bits 4 down to 0 of the arbitration of the transmitter buffer (TXARB4:TXARB0)
TX_Message_0: first 8 bits data of the transmitter buffer
TX_Message_1: second 8 bits data of the transmitter buffer
TX_Message_2: third 8 bits data of the transmitter buffer
TX_Message_3: fourth 8 bits data of the transmitter buffer
TX_Message_4: fifth 8 bits data of the transmitter buffer
TX_Message_5: sixth 8 bits data of the transmitter buffer
TX_Message_6: seventh 8 bits data of the transmitter buffer
TX_Message_7: eighth 8 bits data of the transmitter buffer
RX Message Buffers
The AT7908E CAN controller has three receiver message buffers. The incoming data
frame message will be stored on the message object that matches the incoming ID ( see
filtering functionality). If the incoming ID matches more than one ID of the message
object, the message will be stored in the lowest numbered message object. The incom-
ing remote request is not stored on the message buffer.
The structure of the message buffer is:
RXn_STATUS: Status register of the message object n
RXn_ARB0: bits 28 down to 21 of the arbitration of the message object n
RXn_ARB1: bits 20 down to 13 of the arbitration of the message object n
RXn_ARB2: bits 12 down to 5 of the arbitration of the message object n
RXn_ARB3: bits 4 down to 0 of the arbitration of the message object n
RXn_Message_0: first 8 bits data of the message object n
RXn_Message_1: second 8 bits data of the message object n
RXn_Message_2: third 8 bits data of the message object n
RXn_Message_3: fourth 8 bits data of the message object n
RXn_Message_4: fifth 8 bits data of the message object n
RXn_Message_5: sixth 8 bits data of the message object n
14
AT7908E
4268D–AERO–11/09
ATMEL [ ATMEL ]
