Preface
MPC5565 Microcontroller Reference Manual, Rev. 1.0
21-24
Freescale Semiconductor
21.4
Functional Description
21.4.1
Overview
The FlexCAN2 module is a CAN protocol engine with a very flexible message buffer configuration
scheme. The module can have up to 64 message buffers, any of which can be assigned as either a TX buffer
or an RX buffer. Each message buffer has an assigned interrupt flag to indicate successful completion of
transmission or reception.
21.4.2
Transmit Process
The CPU prepares a message buffer for transmission by executing the following steps:
•
Write the CODE field of the control and status word to keep the TX MB inactive (code = 1000).
•
Write the ID word.
•
Write the DATA bytes.
•
Write the LENGTH, SRR, IDE, RTR, and CODE fields of the control and status word to activate
the TX MB.
The first and last steps are mandatory.
21.4.2.1
Arbitration Process
This process selects which will be the next MB to be transmitted. All MBs programmed as transmit buffers
will be scanned to find the lowest ID
1
or the lowest MB number, depending on the LBUF bit in the
CAN
x
_CR. The selected MB will be transferred to an internal serial message buffer (SMB), which is not
user accessible, and then transmitted.
Table 21-16. CAN
x
_IFRL Field Descriptions
Field
Description
0–31
BUF
n
I
Message buffer
n
interrupt. Each bit represents the respective FlexCAN2 message buffer (MB31 to MB0)
interrupt. Write 1 to clear.
0 No such occurrence
1 The corresponding buffer has successfully completed transmission or reception.
1. Actually, if LBUF is negated, the arbitration considers not only the ID, but also the RTR and IDE bits placed inside the ID at the
same positions they are transmitted in the CAN frame.
Содержание MPC5565
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