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Chapter 13
FCAN Interface Function
Preliminary User’s Manual U14913EE1V0UM00
13.2.7 Mask
handling
The FCAN system supports two concepts of message reception, the BasicCAN concept and the Full-
CAN concept.
In the Full-CAN concept a particular message buffer accepts only one single message, hence there is
no further sorting and filtering required by software. As a consequence only one unambiguous identifier
is assigned to a message buffer.
In the BasicCAN concept a receive message buffer operates as a channel, which can accept several
messages. After reception software must sort, respectively filter, which particular message has been
received.
By the usage of hardware masks the range of receive messages can be limited to reduce the CPU load
caused by message sorting.
In the FCAN system each CAN module provides 4 different masks.
For a receive message buffer assigned to a CAN module one of the 4 masks can be selected when the
BasicCAN concept is used.
When using a mask, a certain identifier value must be written into the identifier register M_IDm (equals
32 bit value build by M_IDHm and M_IDLm) of the receive message buffer at initialisation.
Then the linked mask CxMASKn composed from CxMASKHn and CxMASKLn determines which iden-
tifier bits of a received message must match exactly to accept the received message for the message
buffer.
The mask facilitates that certain identifier bits of the received message will not be compared with the
corresponding identifier bits of the message buffer, thus several messages might be accepted for the
receive message buffer.
Remarks: 1. n = 0 to 3
2. m = 00 to 63
3. x = 1 to 3
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