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Chapter 14
FCAN Interface Function
Preliminary User’s Manual U15839EE1V0UM00
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Message reception
Due to the vast initialisation possibilities for each message buffer in the FCAN system, it is possi-
ble that a received message fits in several message buffers assigned to a CAN module.
A fixed rule according to the priority classes has been implemented to avoid arbitrary message
storage and uncontrolled behaviour.
The storage priority for data frames and for remote frames is different (refer to Table 14-12 and
Table 14-13).
Table 14-12:
Storage Priority for Reception of Data Frames
Table 14-13:
Storage priority for Reception of Remote Frames
Caution:
A priority class with lower priority don’t provide a backup for classes with higher pri-
ority. That means that a message (i.e. data frame / remote frame) is explicitly stored
in the priority class with higher priority and never stored in the lower prior class.
Example:
Two receive message buffers are linked to CAN module 1:
• Buffer 1: non-masked receive buffer with identifier ID
K
• Buffer 2: receive buffer with ID
K
linked to mask 2.
Under that configuration a message with ID
K
is never stored in the receive buffer linked to mask 2,
but always into the non-masked receive buffer.
Furthermore, there is a fixed inner storage rule in case several buffers of the same priority class
are linked to a CAN module. For the inner priority class storage rule the data new flag (DN) in the
M_STATm register is the first storage criteria (m = 00 to 31).
Whenever the DN flag cannot provide an unambiguous criteria for storing the message (i.e. there
are several message buffers of the same priority class with DN flag set or not set) the physical
message buffer number is chosen as the second criteria.
Priority Class
Condition
1 (high)
received data frame fits in non-masked receive buffer
2
received data frame fits in receive buffer linked to mask 0
3
received data frame fits in receive buffer linked to mask 1
4
received data frame fits in receive buffer linked to mask 2
5 (low)
received data frame fits in receive buffer linked to mask 3
Priority Class
Condition
1 (high)
received remote frame fits in transmit buffer
2
received remote frame fits in non-masked receive buffer
3
received remote frame fits in receive buffer linked to mask 0
4
received remote frame fits in receive buffer linked to mask 1
5
received remote frame fits in receive buffer linked to mask 2
6 (low)
received remote frame fits in receive buffer linked to mask 3
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