Chapter 11. I˛C
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Chapter 11. I˛C

I˛C is a bi-directional two-wire (data and clock) serial bus that provides a communication link between integrated circuits. Examples of simple I˛C-compatible devices found in embedded systems include EEPROMs, thermal sensors, and real-time clocks.

ZDev provides I˛C master driver APIs to access I˛C devices. The I˛C functions are declared in i2c.h. The following example measures the distance using SRF02, an I˛C based ultra sonic range finder.

Listing 11.1. Distance measurement with SRF02

#include <board.h>
#include <delay.h>
#include <i2c.h>

int main()
{
        int distance;
        /* The 7-bit I2C address from datasheet. */
        uint8_t addr = 0x78;
        uint8_t buf[2];

        board_init();
        board_stdout(LCD_STDOUT);

        delay_init();
        lcd_init();
        i2c_init();

        while(1) {
                /*
                 * Write 0x51 to register 0x0.
                 * Starts real ranging in cm.
                 */
                buf[0] = 0x0;
                buf[1] = 0x51;
                i2c_tx(addr, buf, 2);
                mdelay(66);

                /*
                 * Read 0x2 and 0x3 to get the
                 * distance hi-byte and low-byte.
                 */
                buf[0] = 0x2;
                i2c_tx(addr, buf, 1);
                i2c_rx(addr, buf, 2);

                distance = ((buf[0] << 8) + buf[1]);
                printf("Range = %dcm\n", distance);

                mdelay(1000);
        }
}

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