void write_flash( unsigned char dat,unsigned char xdata *ptr )
  {
   unsigned char xdata *pwrite;
   char EA_save,PCA0MD_save;

     // Disable Watchdog timer
   PCA0MD_save=PCA0MD;
   PCA0MD &= ~0x40;                    // WDTE = 0 (clear watchdog timer
                                       // enable)

   // erase the FLASH page at 0x1000
   EA_save = EA;
   EA = 0;                             // disable interrupts (precautionary)

   // initialize write/erase pointer
   pwrite = ptr;
   PSCTL = 0x03;                       // MOVX writes erase FLASH page

   FLKEY = 0xA5;                       // FLASH lock and key sequence 1
   FLKEY = 0xF1;                       // FLASH lock and key sequence 2
   *pwrite = 0;                        // initiate page erase

   PSCTL = 0;                          // MOVX writes target XRAM

   // copy a dat FLASH memory at address ptr

   pwrite = ptr;                    // initialize FLASH write pointer
   PSCTL = 0x01;                    // MOVX writes target FLASH memory

   FLKEY = 0xA5;                    // FLASH lock and key sequence 1
   FLKEY = 0xF1;                    // FLASH lock and key sequence 2
   *pwrite = dat;                   // copy byte

   PSCTL = 0x00;                    // MOVX writes target XRAM
   EA = EA_save;                    // re-enable interrupts
   PCA0MD=PCA0MD_save;
  }

#define InternalFLASHAddress 0x7A00    // Адрес начала области для хранения параметров
#define SYSTEM_PARAMETERS_SIZE 190     // Размер области для хранения системных параметров

xdata unsigned char InternalBuffer[SYSTEM_PARAMETERS_SIZE]; //Внутренний буфер для параметров

void WriteToInternalFlash(unsigned char *ptr)
{
    unsigned char xdata *FlashPointToWrite;     //Указатель на 512-байтную область памяти
    idata unsigned char index;
    FlashPointToWrite = InternalFLASHAddress;
    
    FLSCL = 0x88;                         // set FLASH scale register for 12000000Hz system clock
    PSCTL = 0x03;                         // set PSWE and PSEE to ‘1’s (MOVX instructions erase the corresponding FLASH page)
    *FlashPointToWrite = 0;                     // initiate the erase cycle
    PSCTL = 0x01;                         // clear PSEE, leaving PSWE set to ‘1’. MOVX instructions will write to the corresponding FLASH address.
    for (index=0;index<SYSTEM_PARAMETERS_SIZE;index++)
       *(FlashPointToWrite++) = *(ptr+index);
    PSCTL = 0;                                     
    FLSCL = 0x8f;                                     
    return;
}

void main(void)
{
// .....
    WriteToInternalFlash(&InternalBuffer[0]);
// ....
}