70353C Datasheet, PDF(45/76 Page) Microchip Technology – Section 21. Enhanced Controller Area Network

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70353C Datasheet, PDF (45/76 Pages) Microchip Technology – Section 21. Enhanced Controller Area Network

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Section 21. Enhanced Controller Area Network (ECANâ¢)

21.7.1.2 ACCEPTANCE FILTER MASKS

As shown in Figure 21-11 and Figure 21-12, an acceptance filter mask determines which bits in

the incoming message identifiers are examined with the acceptance filters.

The acceptance filters optionally select one of the Acceptance filter masks using the Mask

Source Select (FnMSK<1:0>) mask select bits in the CiFMSKSEL1 and CiFMSKSEL2 registers:

â¢ CiFMSKSEL1: ECAN Filter 7-0 Mask Selection Register

â¢ CiFMSKSEL2: ECAN Filter 15-8 Mask Selection Register

The selection values for the FnMSK<1:0> bit are:

â¢ 11 = Reserved

â¢ 10 = Select acceptance filter mask 2

â¢ 01 = Select acceptance filter mask 1

â¢ 00 = Select acceptance filter mask 0

Table 21-1 is a truth table that indicates how each bit in the identifier is compared to the masks

and filters to determine if the message should be accepted or rejected. The mask bit essentially

determines which bits to apply the filter to. If any mask bit is set to â0â, that bit is automatically

accepted, regardless of the filter bit.

Table 21-1: Acceptance Filter/Mask Truth Table

Mask (SIDn/EIDn) Filter (SIDn/EIDn) Message (SIDn/EIDn)

Accept or Reject bit n

Reject

21.7.1.3 MESSAGE TYPE SELECTION

The Extended Identifier Enable bit (EXIDE) in the ECAN Acceptance Filter n Standard

Identifier register (CiRXFnSID<3>) enables reception of either SID or EID messages. The

Identifier Receive Mode bit (MIDE) in the ECAN Acceptance Filter Mask n SID register

(CiRXMnSID<3>) enables the EXIDE bit. If the MIDE bit is set, only the type of message selected

by the EXIDE bit is accepted. If the MIDE bit is clear, the EXIDE bit is ignored and all messages

that match the filter are accepted.

Table 21-2: Message Type Selections

EXIDE MIDE

Selection

1 Acceptance filter to check for SID

1 Acceptance filter to check for EID

0 Acceptance filter to check for SID/EID

21.7.1.4 ACCEPTANCE FILTER CONFIGURATION

A sample code used to configure the acceptance filter 0 to receive the SID messages using the

acceptance filter mask register to mask SID<2:0> bits is shown in Example 21-4.

DS70353C-page 21-45

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