MAC7200 datasheet(606/976 Pages) FREESCALE

606 / 976 page

The Generic FlexCAN2 Module

MAC7200 Microcontroller Family Reference Manual, Rev. 2

528

Freescale Semiconductor

NOTE

The individual Rx Mask per Message Buffer feature may not be available in

low cost MCUs. Please consult the specific MCU documentation to find out

if this feature is supported. If not supported, the RXGMASK, RX14MASK

and RX15MASK registers are available, regardless of the value of the BCC

bit.

28.2.7

Functional Description

28.2.7.1

Overview

The FlexCAN module is a CAN protocol engine with a very flexible mailbox system for transmitting and

receiving CAN frames. The mailbox system is composed by a set of up to 64 Message Buffers (MB) that

store configuration and control data, time stamp, message ID and data (see Section 28.2.6.2, “Message

Buffer Structure”). Any MB can be work as a transmission or reception buffer. An arbitration algorithm

decides the prioritization of MBs to be transmitted based on either the message ID or the MB ordering. A

matching algorithm makes it possible to store received frames only into MBs that have the same ID

programmed on its ID field. A masking scheme makes it possible to match the ID programmed on the MB

with a range of IDs on received CAN frames. A reception queue can be implemented by programming the

same ID on more than one receiving MB. Data coherency mechanisms are implemented to guarantee data

integrity during MB manipulation by the CPU.

Before proceeding with the functional description, an important concept must be explained. A Message

Buffer is said to be “active” at a given time if it can participate in the matching and arbitration algorithms

that are happening at that time. An Rx MB with a ‘0000’ code is inactive (refer to Table 28-7). Similarly,

a Tx MB with a ‘1000’ code is also inactive (refer to Table 28-8). An MB not programmed with either

‘0000’ or ‘1000’ will be temporarily deactivated (will not participate in the current arbitration/matching

Address: Base + $0880–$097F

MI28

MI27

MI26

MI25

MI24

MI23

MI22

MI21

MI20

MI19

MI18

MI17

MI16

9876543210

MI15

MI14

MI13

MI12

MI11

MI10

MI9

MI8

MI7

MI6

MI5

MI4

MI3

MI2

MI1

MI0

Figure 28-11. Rx Individual Mask Registers (RXIMR0–RXIMR63)

Table 28-15. RXIMRn Field Descriptions

Field

Description

31–29

Reserved.

28–18

MI28–MI18

Standard ID Mask Bits. These bits are the same mask bits for the Standard and Extended Formats.

17–0

MI17–MI0

Extended ID Mask Bits. These bits are used to mask comparison only in Extended Format.

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