70353C datasheet(57/76 Pages) MICROCHIP

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DS70353C-page 21-57

Section 21. Enhanced Controller Area Network (ECAN™)

21.8

DMA CONTROLLER CONFIGURATION

The ECAN module uses device RAM for the message buffers to support both transmission and

reception of CAN messages. The number of message buffers to be used by the ECAN module

is specified by the DMA Buffer Size bits (DMABS<2:0>) in the ECAN FIFO Control register

(CiFCTRL<15:13>). The DMAxSTAL and DMAxSTAH registers in the DMA controller defines the

start of the CAN buffer area. The DMA controller moves data between ECAN and the message

buffers (placed in device RAM) without CPU intervention.

21.8.1

DMA Operation for Transmitting Data

The user application selects a message for transmission by setting the Message Send

Request bit (TXREQ) in the ECAN TX/RX Buffer m or n Control register (CiTRmnCON<3>).

The ECAN controller uses DMA to read the message from the message buffer and transmit the

message. The ECAN module generates a transmit data interrupt to start a DMA cycle. In

response to the interrupt, the DMA channel that is configured for ECAN message transmission

reads from the message buffer in device RAM and stores the message in the ECAN Transmit

Data register (CiTXD). Eight words are transferred for every message transmitted by the ECAN

controller. The detailed layout of the transmit message buffer is provided in 21.2 “CAN

Message Formats”. A sample code for configuring the DMA channel for ECAN1 transmission

is shown in Example 21-6.

Example 21-6:

DMA Channel 0 Configuration for ECAN1 Transmission

Note:

For more information on configuring and using the DMA module, refer to Section

22. “Direct Memory Access (DMA)” (DS70348) of the “dsPIC33E/PIC24E Family

Reference Manual”, which is available from the Microchip web site

(www.microchip.com).

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

transmission. Refer to Example 21-1 for an application example */

/* Data Transfer Size: Word Transfer Mode */

DMA0CONbits.SIZE = 0x0;

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

DMA0CONbits.DIR = 0x1;

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

DMA0CONbits.AMODE = 0x2;

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

DMA0CONbits.MODE = 0x0;

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

DMA0REQ = 70;

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

DMA0CNT = 7;

/* Peripheral Address: ECAN1 Transmit Register */

DMA0PAD = (volatile unsigned int); & CITxD;

unsigned long address;

DMA1STAL = (unsigned int) &ecan1msgBuf;

DMA1STAH = (unsigned int) &ecan1msgBuf;

/* Channel Enable: Enable DMA Channel 0 */

DMA0CONbits.CHEN = 0x1;

/* Channel Interrupt Enable: Enable DMA Channel 0 Interrupt */

IEC0bits DMA0IE = 1;

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