STM32F4_I2C_CR1_POS
cr1 &= ~(STM32F4_I2C_CR1_ACK | STM32F4_I2C_CR1_POS);
cr1 |= STM32F4_I2C_CR1_POS;
cr1 &= ~STM32F4_I2C_CR1_POS;