Can Receive Buffer; Table 22-31. Can Receive Buffer - Sharp Blue Treak LH75400 User Manual

Controller Area Network

22.3.2.15 CAN Receive Buffer

The Receive Buffer provides the window through which the CPU accesses the Receive
FIFO. Like the Transmit Buffer, the Receive Buffer has a length of 13 bytes (enough to
accommodate one Receive message of up to eight data bytes).
Read Only access to the Receive Buffer is provided in Operating Mode using CAN offsets
0x40 - 0x70.
The layout of the Receive Buffer is similar to, and compatible with, the Transmit Buffer. It
is essential to distinguish between SFF and EFF messages.
The Receive Buffer is subdivided into descriptor and data fields. The first byte of the descrip-
tor field holds frame information. It describes the frame format (SFF or EFF), specifies
remote or data frame and gives the data length. This is then followed by either two identifier
bytes for SFF messages or four bytes for EFF messages. The data field contains up to eight
data bytes.
22-26

Table 22-31. CAN Receive Buffer

STANDARD FRAME FORMAT
CAN OFFSET
0x40 RX Frame Information
0x44 RX Identifier 1
0x48 RX Identifier 2
0x4C RX Data Byte 1
0x50 RX Data Byte 2
0x54 RX Data Byte 3
0x58 RX Data Byte 4
0x5C RX Data Byte 5
0x60 RX Data Byte 6
0x64 RX Data Byte 7
0x68 RX Data Byte 8
0x6C (Unused)
0x70 (Unused)
LH75400/01/10/11 (Preliminary) User's Guide
EXTENDED FRAME FORMAT
FIELD CAN OFFSET
0x40
0x44
0x48
0x4C
0x50
0x54
0x58
0x5C
0x60
0x64
0x68
0x6C
0x70
6/17/03
FIELD
RX Frame Information
RX Identifier 1
RX Identifier 2
RX Identifier 3
RX Identifier 4
RX Data Byte 1
RX Data Byte 2
RX Data Byte 3
RX Data Byte 4
RX Data Byte 5
RX Data Byte 6
RX Data Byte 7
RX Data Byte 8