UM10360 All information provided in this document is subject to legal disclaimers. © NXP B.V. 2013. All rights reserved.
User manual Rev. 3 — 19 December 2013 347 of 841
NXP Semiconductors
UM10360
Chapter 16: LPC176x/5x CAN1/2
16.5.4 Receive Buffer (RXB)
The Receive Buffer (RXB) represents a CPU accessible Double Receive Buffer. It is
located between the CAN Controller Core Block and APB Interface Block and stores all
received messages from the CAN Bus line. With the help of this Double Receive Buffer
concept the CPU is able to process one message while another message is being
received.
The global layout of the Receive Buffer is very similar to the Transmit Buffer described
earlier. Identifier, Frame Format, Remote Transmission Request bit and Data Length
Code have the same meaning as described for the Transmit Buffer. In addition, the
Receive Buffer includes an ID Index field (see Section 16.7.9.1 “
ID index field”).
The received Data Length Code represents the real transmitted Data Length Code, which
may be greater than 8 depending on transmitting CAN node. Nevertheless, the maximum
number of received data bytes is 8. This should be taken into account by reading a
message from the Receive Buffer. If there is not enough space for a new message within
the Receive Buffer, the CAN Controller generates a Data Overrun condition when this
message becomes valid and the acceptance test was positive. A message that is partly
written into the Receive Buffer (when the Data Overrun situation occurs) is deleted. This
situation is signalled to the CPU via the Status Register and the Data Overrun Interrupt, if
enabled.
Fig 54. Transmit buffer layout for standard and extended frame format configurations
TX Frame info unused TX Priority
0 . . . 0 ID.28 ... ID.18
TX Data 4 TX Data 3 TX Data 2 TX Data 1
TX Data 8 TX Data 7 TX Data 6 TX Data 5
unused
31 24 23 16 15 8 7 0
TFS
TID
TDA
TDB
Descriptor
Field
Data Field
Standard Frame Format (11-bit Identifier)
Frame info unused TX DLC TX Priority
0 0 0 ID.28 ... ID.00
TX Data 4 TX Data 3 TX Data 2 TX Data 1
TX Data 8 TX Data 7 TX Data 6 TX Data 5
unused
31 24 23 16 15 8 7 0
TFS
TID
TDA
TDB
Descriptor
Field
Data Field
Extended Frame Format (29-bit Identifier)
TX DLC
TX
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