70353C datasheet(58/76 Pages) MICROCHIP

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dsPIC33E/PIC24E Family Reference Manual

DS70353C-page 21-58

21.8.2

DMA Operation for Receiving Data

When the ECAN controller completes a received message (eight words), the completed

message is transferred to a message buffer in device RAM by the DMA module. The ECAN

module generates a receive data interrupt to start a DMA cycle. In response to this interrupt, the

DMA channel that is configured for ECAN message reception reads from the ECAN Receive

Data register (CiRXD) and stores the message in the device RAM buffer. Eight words are

transferred for every message that is received by the ECAN controller. The detailed layout of the

received message is provided in 21.2 “CAN Message Formats”. A sample code for configuring

the DMA channel for ECAN1 reception is shown in Example 21-7.

Example 21-7:

DMA Channel 1 Configuration for ECAN1 Reception

Note:

For more information on how to configure the DMA Controller, refer to Section 22.

“Direct Memory Access (DMA)” (DS70348).

/* This code snippet shows an example of configuring a DMA channel for the

ECAN message reception. Refer to Example 21-4 for an application example */

/* Data Transfer Size: Word Transfer Mode */

DMA1CONbits.SIZE = 0x0;

/* Data Transfer Direction: Peripheral to device RAM */

DMA1CONbits.DIR = 0x0;

/* DMA Addressing Mode: Peripheral Indirect Addressing mode */

DMA1CONbits.AMODE = 0x2;

/* Operating Mode: Continuous, Ping-Pong modes disabled */

DMA1CONbits.MODE = 0x0;

/* Assign ECAN1 Receive event for DMA Channel 0 */

DMA1REQ = 34;

/* Set Number of DMA Transfer per ECAN message to 8 words */

DMA1CNT = 7;

/* Peripheral Address: ECAN1 Receive Register */

DMA1PAD = (volatile unsigned int) &C1RXD;

unsigned long address;

DMA1STAL = (unsigned int) &ecan1msgBuf;

DMA1STAH = (unsigned int) &ecan1msgBuf;

/* Channel Enable: Enable DMA Channel 1 */

DMA1CONbits.CHEN = 0x1;

/* Channel Interrupt Enable: Enable DMA Channel 1 Interrupt */

IEC0bits.DMA1IE = 1;

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