DSPIC30F datasheet(107/220 Pages) MICROCHIP

107 / 220 page

 2004 Microchip Technology Inc.

Preliminary

DS70116C-page 105

dsPIC30F5011/5013

17.0

CAN MODULE

17.1

Overview

The Controller Area Network (CAN) module is a serial

interface, useful for communicating with other CAN

modules or microcontroller devices. This interface/

protocol was designed to allow communications within

noisy environments.

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 implemen-

tation 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

• Support for remote frames

• Double-buffered receiver with two prioritized

received message storage buffers (each buffer

may contain up to 8 bytes of data)

• 6 full (standard/extended identifier) acceptance

filters, 2 associated with the high priority receive

buffer and 4 associated with the low priority

receive buffer

• 2 full acceptance filter masks, one each

associated with the high and low priority receive

buffers

• Three transmit buffers with application specified

prioritization and abort capability (each buffer may

contain up to 8 bytes of data)

• 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 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.

17.2

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 desti-

nation node sends a remote frame with an identi-

fier 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 2

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 2 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.

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