spi.c

Explains how to communicate over the SPI bus.

/*
 * This example shows how to read the temperature from the Temp. Sensor module
 * over the SPI.
 */

#include <stm32f4xx.h>
#include <carme.h>
#include <carme_io2.h>

#define DS1722_CONFIG_ADDR  0x80    /* Configuration Register       */

/*
 * Defines for DS1722 configuration
 * Choose a control byte for the DS1722.
 * D7 = always 1
 * D6 = always 1
 * D5 = always 1
 * D4 = one shot (0: continuous, 1: one shot)
 * D3 = Resolution
 * D2 = Resolution
 * D1 = Resolution
 * D0 = shut down (0: continuous, 1: shut down)
 */
#define DS1722_DEFAULT      0xE0    /* Bit 5, 6, 7 always 1         */
#define DS1722_1SHOT        0x10    /* Bit 4 one shot               */
#define DS1722_RES_8BIT     0x00    /* Bit 1,2,3 Resolution 8Bit    */
#define DS1722_RES_9BIT     0x02    /* Bit 1,2,3 Resolution 9Bit    */
#define DS1722_RES_10BIT    0x04    /* Bit 1,2,3 Resolution 10Bit   */
#define DS1722_RES_11BIT    0x06    /* Bit 1,2,3 Resolution 11Bit   */
#define DS1722_RES_12BIT    0x08    /* Bit 1,2,3 Resolution 12Bit   */
#define DS1722_SHUTDOWN     (1<<0)  /* Bit 0 shut down              */

#define DS1722_TEMP_LSB     0x01    /* Data register Temp LSB       */
#define DS1722_TEMP_MSB     0x02    /* Data register Temp MSB       */

int main(void) {

    uint16_t spiData[2];
    uint8_t celsius;

    CARME_IO2_Init();
    CARME_IO2_SPI_Select(CARME_IO2_nPSC1);

    /* Configure the temperature chip */
    CARME_IO2_SPI_CS_Out(Bit_RESET); /* set CS low */
    CARME_IO2_SPI_Send(DS1722_CONFIG_ADDR << 8 | DS1722_DEFAULT | DS1722_RES_9BIT);
    CARME_IO2_SPI_CS_Out(Bit_SET); /* set CS high */

    for (;;) {
        /* Get the temperature */
        CARME_IO2_SPI_CS_Out(Bit_RESET);
        CARME_IO2_SPI_Send(DS1722_TEMP_LSB);
        CARME_IO2_SPI_Receive(&spiData[0]);
        CARME_IO2_SPI_Send(DS1722_TEMP_MSB);
        CARME_IO2_SPI_Receive(&spiData[1]);
        CARME_IO2_SPI_CS_Out(Bit_SET);

        celsius = ((spiData[1] << 8 | spiData[0]) >> 7) / 2;
    }
    return 0;
}