CAN 2.0B Controller Module
MPC561/MPC563 Reference Manual, Rev. 1.2
16-14
Freescale Semiconductor
The user should prepare or change a message buffer for transmission by executing the following steps.
1. Write the control/status word to hold the transmit buffer inactive (code = 0b1000)
2. Write the ID_HIGH and ID_LOW words
3. Write the data bytes
4. Write the control/status word (active Tx code, Tx length)
NOTE
Steps 1 and 4 are mandatory to ensure data coherency.
Once an active transmit code is written to a transmit message buffer, that buffer begins participating in an
internal arbitration process as soon as the receiver senses that the CAN bus is free, or at the inter-frame
space. If there are multiple messages awaiting transmission, this internal arbitration process selects the
message buffer from which the next frame is transmitted.
When this process is over and a message buffer is selected for transmission, the frame from that message
buffer is transferred to the serial message buffer for transmission.
The TouCAN transmits no more than eight data bytes, even if the transmit length contains a value greater
than eight.
At the end of a successful transmission, the value of the free-running timer (which was captured at the
beginning of the identifier field on the CAN bus), is written into the time stamp field in the message buffer.
The code field in the control/status word of the message buffer is updated and a status flag is set in the
IFLAG register.
16.4.3.1
Transmit Message Buffer Deactivation
Any write access to the control/status word of a transmit message buffer during the process of selecting a
message buffer for transmission immediately deactivates that message buffer, removing it from the
transmission process.
If the transmit message buffer is deactivated while a message is being transferred from it to a serial
message buffer, the message is not transmitted.
If the transmit message buffer is deactivated after the message is transferred to the serial message buffer,
the message is transmitted, but no interrupt is requested, and the transmit code is not updated.
If a message buffer containing the lowest ID is deactivated while that message is undergoing the internal
arbitration process to determine which message should be sent, then that message may not be transmitted.
16.4.3.2
Reception of Transmitted Frames
The TouCAN receives a frame it has transmitted if an empty message buffer with a matching identifier
exists.
16.4.4
Receive Process
During the receive process, the following events occur:
Summary of Contents for MPC561
Page 84: ...MPC561 MPC563 Reference Manual Rev 1 2 lxxxiv Freescale Semiconductor...
Page 144: ...Signal Descriptions MPC561 MPC563 Reference Manual Rev 1 2 2 46 Freescale Semiconductor...
Page 206: ...Central Processing Unit MPC561 MPC563 Reference Manual Rev 1 2 3 62 Freescale Semiconductor...
Page 302: ...Reset MPC561 MPC563 Reference Manual Rev 1 2 7 14 Freescale Semiconductor...
Page 854: ...Time Processor Unit 3 MPC561 MPC563 Reference Manual Rev 1 2 19 24 Freescale Semiconductor...
Page 968: ...Development Support MPC561 MPC563 Reference Manual Rev 1 2 23 54 Freescale Semiconductor...
Page 1144: ...Internal Memory Map MPC561 MPC563 Reference Manual Rev 1 2 B 34 Freescale Semiconductor...
Page 1212: ...TPU3 ROM Functions MPC561 MPC563 Reference Manual Rev 1 2 D 60 Freescale Semiconductor...
Page 1216: ...Memory Access Timing MPC561 MPC563 Reference Manual Rev 1 2 E 4 Freescale Semiconductor...