MCP8021 datasheet(45/66 Pages) MICROCHIP

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DS20006265D-page 45

MCP8021/2

5.2.6

AUTO-BAUD CODE EXAMPLE

Example 5-1 is a dsPIC® DSC code example using

the auto-baud function.

EXAMPLE 5-1:

dsPIC® DSC AUTO-BAUD EXAMPLE

// #define FCY 70000000UL

#define TypBaudrate 9600uL

#define U1BRG_BAUDRATE (FCY/(16 * TypBaudrate)) - 1

#define U1BRG_BAUD_MIN

((((FCY/(16 * TypBaudrate)) - 1)*1.07f))

//plus 7%

#define U1BRG_BAUD_MAX

((((FCY/(16 * TypBaudrate)) - 1)*0.93f))

//minus 7%

#define U1BRG_BREAK

(FCY/(16 * 7880uL)) - 1

//7880 baud-rate is midpoint of

//required break window for MCP8021

void UART1_Init(void){

//UART configuration - setup PPS connections

U1MODEbits.UARTEN = 1; // enable UART

//and UART module enable here

}

void UART1_AutoBaud(void){

U1MODEbits.ABAUD = 0;

int lastBRG = U1BRG;

//save last known good BRG value - on POR BRG value

//will be 0x0

U1STAbits.UTXEN = 1;

//Transmit enabled, UxTX pin controlled by UARTx

while(U1STAbits.UTXBF);

//Wait for transmit buffer to empty

while(!U1STAbits.TRMT);

//wait for last byte to finish transmitting

U1BRG = U1BRG_BREAK;

//7880baud representing 1.65ms dominant

//with 13bit BREAK

U1STAbits.UTXBRK = 1;

//Send BREAK command

U1TXREG = 0x00;

//Dummy write to start BREAK command

while (U1STAbits.UTXBRK);

//wait for completion of BREAK sequence

while (!U1STAbits.TRMT);

//wait for last break bit to transmit

U1STAbits.UTXEN = 0;

//disable TX while waiting on 0x55 from MCP8021

U1MODEbits.ABAUD = 1;

//start the ABAUD counter upon receipt of

//next byte (0x55)

while(U1MODEbits.ABAUD);

//application should handle timeout if auto-baud

//does not complete and attempt auto-baud routine again

//verify new baud clock is within limits of MCP8021 min and

//max baud-rate

if ((U1BRG > U1BRG_BAUD_MAX) && (U1BRG < U1BRG_BAUD_MIN)){ //success, use new baud-rate

//generator value

}

else{

U1BRG = lastBRG;

//auto-baud out of range, reload last known good BRG value

//and attempt auto-baud routine again

}

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