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Sheet目录3881

194页 195页 196页 197页 [198页]199页 200页 201页 202页

2004 Microchip Technology Inc.

DS30491C-page 275

PIC18F6585/8585/6680/8680

23.0

ECAN MODULE

PIC18F6585/8585/6680/8680

devices

contain

Enhanced Controller Area Network (ECAN) module.

The ECAN module is fully backward compatible with

the CAN module available in PIC18CXX8 and

PIC18FXX8 devices.

The Controller Area Network (CAN) module is a serial

interface which is useful for communicating with other

peripherals or microcontroller devices. This interface,

or protocol, was designed to allow communications

within noisy environments.

The ECAN module is a communication controller,

implementing the CAN 2.0A or B protocol as defined in

the BOSCH specification. The module will support

CAN 1.2, CAN 2.0A, CAN 2.0B Passive and CAN 2.0B

Active versions of the protocol. The module implemen-

tation is a full CAN system; however, the CAN specifi-

cation is not covered within this data sheet. Refer to the

BOSCH CAN specification for further details.

The module features are as follows:

Implementation of the CAN protocol CAN 1.2,

CAN 2.0A and CAN 2.0B

DeviceNetTM data bytes filter support

Standard and extended data frames

0-8 bytes data length

Programmable bit rate up to 1 Mbit/sec

Fully backward compatible with PIC18XX8 CAN

module

Three modes of operation:

- Mode 0 – Legacy mode

- Mode 1 – Enhanced Legacy mode with

DeviceNet support

- Mode 2 – FIFO mode with DeviceNet support

Support for remote frames with automated handling

Double-buffered receiver with two prioritized

received message storage buffers

Six buffers programmable as RX and TX

message buffers

16 full (standard/extended identifier) acceptance

filters that can be linked to one of four masks

Two full acceptance filter masks that can be

assigned to any filter

One full acceptance filter that can be used as either

an acceptance filter or acceptance filter mask

Three dedicated transmit buffers with application

specified prioritization and abort capability

Programmable wake-up functionality with

integrated low-pass filter

Programmable Loopback mode supports self-test

operation

Signaling via interrupt capabilities for all CAN

receiver and transmitter error states

Programmable clock source

Programmable link to timer module for

time-stamping and network synchronization

Low-Power Sleep mode

23.1

Module Overview

The CAN bus module consists of a protocol engine and

message buffering and control. The CAN protocol

engine automatically handles all functions for receiving

and transmitting messages on the CAN bus. Messages

are transmitted by first loading the appropriate data

registers. Status and errors can be checked by reading

the appropriate registers. Any message detected on

the CAN bus is checked for errors and then matched

against filters to see if it should be received and stored

in one of the two receive registers.

The CAN module supports the following frame types:

Standard Data Frame

Extended Data Frame

Remote Frame

Error Frame

Overload Frame Reception

Interframe Space Generation/Detection

The

CAN

module

uses

the

RG0/CANTX1,

RG1/CANTX2 and RG2/CANRX pins to interface with

the CAN bus. In Normal mode, the CAN module

automatically overrides the TRISG0 and TRISG1 bits

of the CAN module pins.

23.1.1

MODULE FUNCTIONALITY

The CAN bus module consists of a protocol engine,

message buffering and control (see Figure 23-1). The

protocol engine can best be understood by defining the

types of data frames to be transmitted and received by

the module.

The following sequence illustrates the necessary initial-

ization steps before the ECAN module can be used to

transmit or receive a message. Steps can be added or

removed depending on the requirements of the

application.

Ensure that the ECAN module is in Configuration

mode.

Select ECAN Operational mode.

Set up the baud rate registers.

Set up the filter and mask registers.

Set the ECAN module to Normal mode or any

other mode required by the application logic.

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