__delay_ms(1000);
_delay_ms(100);
delay_ms(100);
delay(100);
HAL_Delay(100);
и другие ...

Delay_Ms(100);

#define PCF_I2C_ADDR 0x20
...
void pcf_write(uint8_t data) {
  while(I2C_GetFlagStatus(I2C1, I2C_FLAG_BUSY) != RESET);
  I2C_GenerateSTART(I2C1, ENABLE);

  while(!I2C_CheckEvent(I2C1, I2C_EVENT_MASTER_MODE_SELECT));
  I2C_Send7bitAddress(I2C1, PCF_I2C_ADDR << 1, I2C_Direction_Transmitter);

  while(!I2C_CheckEvent(I2C1, I2C_EVENT_MASTER_TRANSMITTER_MODE_SELECTED));
  if (I2C_GetFlagStatus(I2C1, I2C_FLAG_TXE) != RESET)
    I2C_SendData(I2C1, data);

  while(!I2C_CheckEvent(I2C1, I2C_EVENT_MASTER_BYTE_TRANSMITTED));
  I2C_GenerateSTOP(I2C1, ENABLE);
...
  while(1) {
    pcf_write(0b11111111);
    Delay_Ms(100);
    pcf_write(0b11111110);
    Delay_Ms(100);
  }
}

void SysTick_Handler(void) __attribute__((interrupt("WCH-Interrupt-fast")));