Freescale Semiconductor MCF5480 - Manual (Page 592)

MCF548x Reference Manual, Rev. 3
21-22 Freescale Semiconductor
21.4.2 Message Buffer Memory Map
The message buffer memory map starts at an offset of 0x80 from the FlexCAN’s base address (0xA000 or
0xA800). The 256-byte message buffer space is fully used by the 16 message buffer structures.
Table 21-15. Message Buffer Code for Tx Buffers
RTR Initial Tx Code
Code After
Successful
Transmission
Description
X 1000 — INACTIVE: Message buffer not ready for transmit.
0 1100 1000 Data frame to be transmitted once, unconditionally. After transmission,
the MB automatically returns to the INACTIVE state.
1 1100 0100 Remote frame to be transmitted unconditionally once, and message
buffer becomes an Rx message buffer with the same ID for data frames.
0 1010 1010 Transmit a data frame whenever a remote request frame with the same ID
is received. This message buffer participates simultaneously in both the
matching and arbitration processes. The matching process compares the
ID of the incoming remote request frame with the ID of the MB. If a match
occurs, this message buffer is allowed to participate in the current
arbitration process and the CODE field is automatically updated to 1110
to allow the MB to participate in future arbitration runs. When the frame is
eventually transmitted successfully, the code automatically returns to
1010 to restart the process again.
0 1110 1010 This is an intermediate code that is automatically written to the message
buffer as a result of match to a remote request frame. The data frame will
be transmitted unconditionally once, and then the code will automatically
return to 1010. The CPU can also write this code with the same effect.