Reception Of Can Controller - Fujitsu MB90420/5 (A) Series Hardware Manual

MB90420/5 (A) SERIES F

23.8 Reception of CAN Controller

Reception starts when the start of data frame or remote frame (SOF) is detected on the CAN bus.
n Acceptance filtering
The receive message in the standard frame format is compared with the message buffer (x) set in the
standard frame format (IDEx of the IDE register (IDER) is 0). The receive message in the extended frame
format is compared with the message buffer (x) set (IDEx is 1) in the extended frame format.
If all the bit set to Compare by the acceptance mask match after comparison between the receive message
ID and acceptance code (ID register (IDRx) for comparing with the receive message ID), the receive
message passes through the acceptance filter of the message buffer (x).
n Storing receive message
When the receive operation is successful, receive messages are stored in a message buffer x including IDs
passed through the acceptance filter.
When receiving data frames, receive messages are stored in the ID register (IDRx), DLC register (DLCRx),
and data register (DTRx).
Even if receive message data is less than 8 bytes, some data is stored in the remaining bytes of the DTRx
and its value is undefined.
When receiving remote frames, receive messages are stored only in the IDRx and DLCRx, and the DTRx
remains unchanged.
If there is more than one message buffer including Ids that passed through the acceptance filter, the
message buffer x in which receive messages are to be stored is determined according to the following rules.
• The order of priority of the message buffer x (x = 0 to 15) rises as its number lower; in other words,
message buffer 0 is given the highest priority and the message buffer 15 is given the lowest priority.
• Basically, message buffers with the RCx bit of 0 in the receive completion register (RCR) set to 0 are
preferred in storing receive messages.
• If the bits of the acceptance mask select register (AMSR) are set to All Bits Compare (for message buffers
with the AMSx.1 and AMSx.0 bits set to 00), receive messages are stored irrespective of the value of the
RCx bit of the RCR.
• If there are message buffers with the RCx bit of the RCR set to 0, or with the bits of the AMSR set to all bit
compare, receive messages are stored in the lowest-number (highest-priority) message buffer x.
• If there are no message buffers above-mentioned, receive messages are stored in a lower-number
message buffer x.
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MC-16LX FAMILY 16-BIT MICROCONTROLLERS HARDWARE MANUAL
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