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Sheet目录3873

146页 147页 148页 149页 [150页]151页 152页 153页 154页

2007 Microchip Technology Inc.

Preliminary

DS70165E-page 231

dsPIC33F

20.0

ENHANCED CAN MODULE

20.1

Overview

The Enhanced Controller Area Network (ECAN)

module is a serial interface, useful for communicating

with other CAN modules or microcontroller devices.

This interface/protocol was designed to allow commu-

nications within noisy environments. The dsPIC33F

devices contain up to two ECAN modules.

The CAN module is a communication controller imple-

menting the CAN 2.0 A/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 implementation is

a full CAN system. The CAN specification is not covered

within this data sheet. The reader may 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

Standard and extended data frames

0-8 bytes data length

Programmable bit rate up to 1 Mbit/sec

Automatic response to remote transmission

requests

Up to 8 transmit buffers with application specified

prioritization and abort capability (each buffer may

contain up to 8 bytes of data)

Up to 32 receive buffers (each buffer may contain

up to 8 bytes of data)

Up to 16 full (standard/extended identifier)

acceptance filters

3 full acceptance filter masks

DeviceNet addressing support

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 input capture module (IC2

for both CAN1 and CAN2) for time-stamping and

network synchronization

Low-power Sleep and Idle mode

The CAN bus module consists of a protocol engine and

message buffering/control. The CAN protocol engine

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

receive registers.

20.2

Frame Types

The CAN module transmits various types of frames

which include data messages, or remote transmission

requests initiated by the user, as other frames that are

automatically generated for control purposes. The

following frame types are supported:

Standard Data Frame:

A standard data frame is generated by a node

when the node wishes to transmit data. It includes

an 11-bit Standard Identifier (SID), but not an

18-bit Extended Identifier (EID).

Extended Data Frame:

An extended data frame is similar to a standard

data frame, but includes an extended identifier as

well.

Remote Frame:

It is possible for a destination node to request the

data from the source. For this purpose, the

destination node sends a remote frame with an

identifier that matches the identifier of the required

data frame. The appropriate data source node will

then send a data frame as a response to this

remote request.

Error Frame:

An error frame is generated by any node that

detects a bus error. An error frame consists of two

fields: an error flag field and an error delimiter

field.

Overload Frame:

An overload frame can be generated by a node as

a result of two conditions. First, the node detects

a dominant bit during interframe space which is an

illegal condition. Second, due to internal condi-

tions, the node is not yet able to start reception of

the next message. A node may generate a maxi-

mum of 2 sequential overload frames to delay the

start of the next message.

Interframe Space:

Interframe space separates a proceeding frame

(of whatever type) from a following data or remote

frame.

Note:

This data sheet summarizes the features

of this group of dsPIC33F devices. It is not

intended to be a comprehensive reference

source. To complement the information in

this data sheet, refer to the “dsPIC30F

Family Reference Manual” (DS70046).

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