1.SCLとSDAを接続、プルアップも忘れずに
2.電源の接続
3.下記のソースコードを書き込む
4.コンパイル実行で表示されたら終了
5.おわり
注意
mbedのリビジョンは、143

# include "mbed.h"

# define ADDR        (0x70<<1)  //  address

int main() {

    __HAL_RCC_GPIOA_CLK_ENABLE();
    
    GPIO_InitTypeDef GPIO_InitStruct = {0};
    
    GPIO_InitStruct.Pin = GPIO_PIN_9|GPIO_PIN_10;
    GPIO_InitStruct.Mode = GPIO_MODE_AF_OD;
    GPIO_InitStruct.Pull = GPIO_PULLUP;
    GPIO_InitStruct.Speed = GPIO_SPEED_FREQ_VERY_HIGH;
    GPIO_InitStruct.Alternate = GPIO_AF1_I2C1;
    HAL_GPIO_Init(GPIOA, &GPIO_InitStruct);
    
    GPIO_InitStruct.Pin = GPIO_PIN_4;
    GPIO_InitStruct.Mode = GPIO_MODE_OUTPUT_PP;
    GPIO_InitStruct.Pull = GPIO_NOPULL;
    GPIO_InitStruct.Speed = GPIO_SPEED_FREQ_LOW;
    HAL_GPIO_Init(GPIOA, &GPIO_InitStruct);
    
    __HAL_RCC_I2C1_CLK_ENABLE();


    I2C_HandleTypeDef hi2c1;

    hi2c1.Instance = I2C1;
    hi2c1.Init.Timing = 0x00000708;
    hi2c1.Init.OwnAddress1 = 0;
    hi2c1.Init.AddressingMode = I2C_ADDRESSINGMODE_7BIT;
    hi2c1.Init.DualAddressMode = I2C_DUALADDRESS_DISABLE;
    hi2c1.Init.OwnAddress2 = 0;
    hi2c1.Init.OwnAddress2Masks = I2C_OA2_NOMASK;
    hi2c1.Init.GeneralCallMode = I2C_GENERALCALL_DISABLE;
    hi2c1.Init.NoStretchMode = I2C_NOSTRETCH_DISABLE;
    HAL_I2C_Init(&hi2c1);    
    
    HAL_I2CEx_ConfigAnalogFilter(&hi2c1, I2C_ANALOGFILTER_ENABLE);

    HAL_I2CEx_ConfigDigitalFilter(&hi2c1, 0);

    uint8_t buf[16];

    buf[0]=0x21;
    HAL_I2C_Master_Transmit(&hi2c1, ADDR, buf, 1, 3000);wait_ms(1);

    buf[0]=0x81;
    HAL_I2C_Master_Transmit(&hi2c1, ADDR, buf, 1, 3000);wait_ms(1);

    buf[0]=0xef;
    HAL_I2C_Master_Transmit(&hi2c1, ADDR, buf, 1, 3000);wait_ms(1);

    for(int ii=0;ii<16;ii++){
        buf[0]=ii;
        buf[1]=0x00;
        HAL_I2C_Master_Transmit(&hi2c1, ADDR, buf, 2, 3000);wait_ms(1);
    }//for
    
    while(1) {
            
        for(int ii=0;ii<8;ii++){

            buf[0]=0;
            buf[1]= (1<<ii);
            HAL_I2C_Master_Transmit(&hi2c1, ADDR, buf, 2, 3000);wait_ms(600);

            HAL_GPIO_WritePin(GPIOA, GPIO_PIN_4, GPIO_PIN_SET);
            wait(0.2);
            HAL_GPIO_WritePin(GPIOA, GPIO_PIN_4, GPIO_PIN_RESET);
            wait(0.2);

        }//for
    }//while
}//main