AN1077 View Datasheet(PDF) - STMicroelectronics
Part Name
Description
MFG CO.
'AN1077' PDF : 14 Pages View PDF
OVERVIEW OF ENHANCED CAN CONTROLLERS FOR ST7 AND ST9 MCUS
s Eases the software development evaluation, as even if the CAN bus traffic is not well
defined at the beginning of the project, changes will not impact the CPU behaviour
s Eases the integration of this ECU in a new system To fulfil this requirement the bxCAN
Controller provides eight configurable and scalable filters to the application, in order to
receive only the messages the application needs.
Scalable Width
To optimise and adapt the filters to the application needs, each filter can be scaled independ-
ently. The following combinations are possible:
s One 32 bit filter for filtering the STDID[10:0], IDE, EXTID[17:0] and RTR bits.
s Two16 bit filters for filtering the STDID[10:0], RTR and IDE bits.
s Four 8 bit filters for filtering the STDID[10:3] bits. The other bits are considered as don’t
care.
s One 16 bit filter and two 8 bit filters.
Furthermore each filter can be configured in mask mode or in identifier list mode.
Mask mode
In mask mode the identifier registers are associated with mask registers specifying which bits
of the identifier are handled as “must match” or as “don’t care”. This mode is well suited for se-
lecting a group of identifiers, for instance network management messages.
Identifier List mode
In identifier list mode the mask registers are used as identifier registers. Thus, instead of de-
fining an identifier and a mask, two identifiers are specified, doubling the number of config-
urable single identifiers. All bits of the incoming identifier must match with the bits specified in
the filter registers. This mode is well suited for application messages as their identifiers are
quite “randomly” distributed.
Filter Configuration
While the scale and mode configuration must be done during the initialization of bxCAN, the
value of the identifiers and masks registers can be modified on the fly.
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