FlexCAN Module
MCF5253 Reference Manual, Rev. 1
25-20
Freescale Semiconductor
Table 25-12. Message Buffer Code for Rx Buffers
Rx Code
BEFORE
Rx New Frame
Description
Rx Code
AFTER
Rx New Frame
Comment
0000
INACTIVE:
MB is not active
–
MB does not participate in the matching process.
0100
EMPTY:
MB is active and empty
0010
MB participates in the matching process. When a frame is received
successfully, the code is automatically updated to FULL.
0010
FULL:
MB is full
0010
The act of reading the control & status (C/S) word followed by
unlocking the MB does not make the code return to EMPTY. It remains
FULL. If a new frame is written to the MB after the C/S word was read
and the MB was unlocked, the code still remains FULL.
0110
If the MB is FULL and a new frame should be written into this MB
before the CPU had time to read it, the MB is overwritten, and the code
is automatically updated to OVERRUN.
0110
OVERRUN:
A frame was overwritten
into a full buffer
0010
If the code indicates OVERRUN but the CPU reads the C/S word and
then unlocks the MB, when a new frame is written to the MB, the code
returns to FULL.
0110
If the code already indicates OVERRUN, and yet another new frame
must be written, the MB will be overwritten again, and the code will
remain OVERRUN.
0XY1
1
1
Note that for transmit message buffers (see
), the BUSY bit should be ignored upon read.
BUSY:
Flexcan is updating the
contents of the MB with
a new receive frame.
The CPU should not try
to access the MB.
0010
An EMPTY buffer was written with a new frame (XY was 01).
0110
A FULL/OVERRUN buffer was overwritten (XY was 11).
Table 25-13. Message Buffer Code for Tx Buffers
MBn[RTR]
Initial
Tx Code
Code After
Successful
Transmission
Description
X
1000
–
INACTIVE: Message buffer not ready for transmit and will participate in the arbitration
process.
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.
Summary of Contents for MCF5253
Page 1: ...Document Number MCF5253RM Rev 1 08 2008 MCF5253 Reference Manual...
Page 26: ...MCF5253 Reference Manual Rev 1 xxvi Freescale Semiconductor...
Page 32: ...MCF5253 Reference Manual Rev 1 xxxii Freescale Semiconductor...
Page 46: ...MCF5253 Introduction MCF5253 Reference Manual Rev 1 1 14 Freescale Semiconductor...
Page 62: ...Signal Description MCF5253 Reference Manual Rev 1 2 16 Freescale Semiconductor...
Page 98: ...Instruction Cache MCF5253 Reference Manual Rev 1 5 10 Freescale Semiconductor...
Page 104: ...Static RAM SRAM MCF5253 Reference Manual Rev 1 6 6 Freescale Semiconductor...
Page 128: ...Synchronous DRAM Controller Module MCF5253 Reference Manual Rev 1 7 24 Freescale Semiconductor...
Page 144: ...Bus Operation MCF5253 Reference Manual Rev 1 8 16 Freescale Semiconductor...
Page 176: ...System Integration Module SIM MCF5253 Reference Manual Rev 1 9 32 Freescale Semiconductor...
Page 198: ...Analog to Digital Converter ADC MCF5253 Reference Manual Rev 1 12 6 Freescale Semiconductor...
Page 246: ...DMA Controller MCF5253 Reference Manual Rev 1 14 18 Freescale Semiconductor...
Page 282: ...UART Modules MCF5253 Reference Manual Rev 1 15 36 Freescale Semiconductor...
Page 344: ...Audio Interface Module AIM MCF5253 Reference Manual Rev 1 17 46 Freescale Semiconductor...
Page 362: ...I2 C Modules MCF5253 Reference Manual Rev 1 18 18 Freescale Semiconductor...
Page 370: ...Boot ROM MCF5253 Reference Manual Rev 1 19 8 Freescale Semiconductor...
