MAC7200 datasheet(577/976 Pages) FREESCALE

577 / 976 page

MAC7200 Microcontroller Family Reference Manual, Rev. 2

Freescale Semiconductor

499

Chapter 28

FlexCAN2

28.1

FlexCAN2 Implementation on the MAC7200

28.1.1

Introduction

The FlexCAN2 module complies to the CAN2.0B specification and therefore supports transfer rates of up

to 1Mbit for high speed CAN networks.

On the MAC7200 family of devices, the clock source for the FlexCAN2 can be selected to be either

derived from the PLL clock, or the oscillator clock. Each CAN module in the MAC7200 family of devices

contains 32 mailboxes.

Each of the FlexCAN2 modules can be independently disabled by writing to the MDIS bit in the modules

MCR register. Disabling the module will turn off the clock to the modules protocol engine and message

buffers, although most of the modules registers remain available to be accessed by the core across the

peripheral bus. The MDIS bit is intended to be used when the module is not required in the application.

By default the FlexCANs are disabled after reset (MDIS=1), so, prior to use, the MDIS bit must be cleared.

Unlike most of the other peripherals on the MAC72xx, the CAN modules are not masters. This means that

data coming into the MAC72xx on a CAN interface may not be under the software control of the

MAC72xx. For this reason, it is necessary for the CAN Message ID (i.e.-IDENTIFIER) to be extracted

from a CAN frame for the processor to react to it correctly. The FlexCAN module does this, and stores the

message corresponding to a particular Message ID in a particular mailbox (up to a limit of 32 mailboxes).

See Section 28.2, “The Generic FlexCAN2 Module” for generic information on the Flexible CAN

Module.

28.1.2

Features of FlexCAN2 on MAC7200

•

Memory Map: 32-bit peripheral with 8 bytes, byte/halfword/word addressable

•

Full implementation of the CAN 2.0 protocol specification.

•

Programmable bit rate up to 1Mbps.

•

32 flexible Mail Boxes of 0-8 bytes data length on all modules.

•

All Mail Boxes configurable for either Rx/Tx.

•

Unused Mail Boxes space can be used as general purpose RAM.

•

Supports standard or extended messages.

•

“Time Stamp”, based on a 16-bit free-running counter.

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