uno_i2c_master_example.ino

#include <Wire.h>

#define I2C_SLAVE_ADDRESS 0x19 // the 7-bit address

#define CMD_LED_ON       0xA0
#define CMD_LED_OFF      0xA1
#define CMD_ADD_NUM      0xB0
#define CMD_GET_RESULT   0xB1

void setup() 
{
    Wire.begin();
    Serial.begin(115200);
}


void loop() 
{
    Wire.beginTransmission(I2C_SLAVE_ADDRESS);
    Wire.write(CMD_LED_ON);
    Wire.endTransmission();
    delay(20);

    Wire.beginTransmission(I2C_SLAVE_ADDRESS);
    Wire.write(CMD_LED_OFF);
    Wire.endTransmission();
    delay(1980);

    uint16_t x = random(0, 0x7fff);
    uint16_t y = random(0, 0x7fff);
    uint8_t txbuffer[4];
    txbuffer[0] = (x >> 8);
    txbuffer[1] = (x & 0xff);
    txbuffer[2] = (y >> 8);
    txbuffer[3] = (y & 0xff);

    Wire.beginTransmission(I2C_SLAVE_ADDRESS);
    Wire.write(CMD_ADD_NUM);
    for (int i = 0; i < 4; i++) {
        Wire.write(txbuffer[i]);
    }
    Wire.endTransmission();

    uint8_t rxbuffer[2];
    Wire.beginTransmission(I2C_SLAVE_ADDRESS);
    Wire.write(CMD_GET_RESULT);
    Wire.endTransmission();
    Wire.requestFrom(I2C_SLAVE_ADDRESS, 2);
    rxbuffer[0] = Wire.read();
    rxbuffer[1] = Wire.read();
    uint16_t sum = (rxbuffer[0] << 8) | rxbuffer[1];

    Serial.print(x);
    Serial.print(" + ");
    Serial.print(y);
    Serial.print(" = ");
    Serial.println(sum);
}