STM32 8-bit IO operation

The bottom line is that it is a matter of reading and writing the eight IO ports. You can either write two functions, WriteData() and ReadData(), or call the GPIO bit manipulation functions separately.
void WriteData（u8 data）
{
   // Operate the IO ports connected to the LCD separately, in the order from high to low
    GPIO_WriteBit(GPIO number, Pin number, (data & 0x80) >> 7 ); 
    GPIO_WriteBit(GPIO number, Pin number, (data & 0x40) >> 6 ); 
    GPIO_WriteBit(GPIO number, Pin number, (data & 0x20) >> 5 ); 
    GPIO_WriteBit(GPIO number, Pin number, (data & 0x10) >> 4 ); 
    GPIO_WriteBit(GPIO number, Pin number, (data & 0x08) >> 3 ); 
    GPIO_WriteBit(GPIO number, Pin number, (data & 0x04) >> 2 ); 
    GPIO_WriteBit(GPIO number, Pin number, (data & 0x02) >> 1 ); 
    GPIO_WriteBit(GPIO number, Pin number, data & 0x01);
 }
u8 ReadData (void)
{
   u8 data;
   data = GPIO_ReadInputDataBit (GPIO number, Pin number); //8-bit
   data << 1;
   data |= GPIO_ReadInputDataBit (GPIO number, Pin number); //7-bit
   data << 1;
   data |= GPIO_ReadInputDataBit (GPIO number, Pin number); //6-bit
   data << 1;
   data |= GPIO_ReadInputDataBit (GPIO number, Pin number); //5-bit
   data << 1;
   data |= GPIO_ReadInputDataBit (GPIO number, Pin number); //4-bit
   data << 1;
   data |= GPIO_ReadInputDataBit (GPIO number, Pin number); //3-bit
   data << 1;
   data |= GPIO_ReadInputDataBit (GPIO number, Pin number); //2-bit
   data << 1;
   data |= GPIO_ReadInputDataBit(GPIO number, Pin number); //1 bit
   return data;
  }
With the read and write functions, the rest is the data interaction with the LCD controller.