70353C datasheet(3/76 Pages) MICROCHIP

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DS70353C-page 21-3

Section 21. Enhanced Controller Area Network (ECAN™)

Figure 21-2 illustrates the general structure of the ECAN module and its interaction with the DMA

Controller and device RAM.

Figure 21-2:

ECAN™ Interaction with DMA

21.1.1

ECAN Module

The ECAN module consists of a protocol engine, message acceptance filters, and separate

transmit and receive DMA interfaces. The protocol engine transmits and receives messages to

and from the CAN bus (as per the CAN Specification 2.0B protocol). The user-configurable

acceptance filters are used by the ECAN module to examine the received message and

determine if it should be stored in the DMA message buffer or discarded.

For received messages, the receive DMA interface generates a receive data interrupt to initiate

a DMA cycle. The receive DMA channel reads data from the CiRXD register and writes it into the

message buffer.

For transmit messages, the transmit DMA interface generates a transmit data interrupt to start a

DMA cycle. The transmit DMA channel reads from the message buffer and writes to the CiTXD

21.1.2

Message Buffers

The ECAN module supports up to 32 message buffers for storing data transmitted or received on

the CAN bus. These buffers can be located anywhere in device RAM (start address of the buffer

may be needed to be aligned on an address boundary). Message buffers 0-7 can be configured

for either transmit or receive operation. Message buffers 8-31 are receive-only buffers and

cannot be used for message transmission.

21.1.3

DMA Controller

The DMA controller acts as an interface between the message buffers and ECAN to transfer data

back and forth without CPU intervention. The DMA controller supports up to 15 channels for

transferring data between the device RAM and the dsPIC33E/PIC24E device peripherals. Two

separate DMA channels are required to support the CAN message transmission and the CAN

message reception.

Each DMA channel has a DMA Request register (DMAxREQ), which is used by the user

application to assign an interrupt event to trigger a DMA-based message transfer.

CiTX

CiRX

Message Buffer 0

Message Buffer 7

Message Buffer 8

Message Buffer 31

CAN

Protocol

Engine

ECAN

Transmit

(CiTXD)

Acceptance

Filter 0-15

ECAN

Receive

(CiRXD)

TX DMA

Interface

RX DMA

Interface

DMA

Channel

DMA

Channel

Message Buffer 1

ECAN™ Module

Message Buffer

(Device RAM)

Request

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