snippet of writing to EEPROM

write_eeprom.c

void write_eeprom(uint16_t addr, uint8_t data)
{
  // first read the data on the current address, if it's the same we can save some time
  HAL_GPIO_WritePin(CPU_CTRL_PORT, CPU_MREQ_PIN, LOW);
  HAL_GPIO_WritePin(CPU_CTRL_PORT, CPU_RD_PIN, LOW);
  HAL_GPIO_WritePin(CPU_CTRL_PORT, CPU_WR_PIN, HIGH);
  uint8_t exsiting_byte = CPU_DATA_PORT->IDR & 0xff;

  if(exsiting_byte == data)
    return;

  // if not the same, set up write by disabling read
  HAL_GPIO_WritePin(CPU_CTRL_PORT, CPU_RD_PIN, HIGH);
  // put address on bus first since it's latched on falling edge of 'WR
  CPU_ADDR_PORT->ODR = addr;
  HAL_GPIO_WritePin(CPU_CTRL_PORT, CPU_WR_PIN, LOW);
  data_output();
  CPU_DATA_PORT->ODR = data;
  // data latched on rising edge of 'WR
  HAL_GPIO_WritePin(CPU_CTRL_PORT, CPU_WR_PIN, HIGH);
  // switch back to input and keep polling to see if write is complete
  data_input();
  HAL_GPIO_WritePin(CPU_CTRL_PORT, CPU_RD_PIN, LOW);
  while(1)
  {
    exsiting_byte = CPU_DATA_PORT->IDR;
    if(exsiting_byte == data)
      break;
  }
}