How do I know which flash page to erase to subsequently write to it?

Thanks for your replies.

So far I have been able to erase a page and write a byte to that page; however, I have only been able to implement one function at the time, when I try to call both functions it seems that only the function that is called first is executed. I have included both of the functions to see if somebody can tell me why they are not executing when they are called one after the other.

Thanks

void FLASH_ByteWrite (void)
{
        unsigned char xdata * pwrite;           // FLASH write pointer

        pwrite = (unsigned char xdata *) FLASH_WRITE_READ_ERASE;
        PSCTL = 0x01;     // PSWE = 1 which enables writes
        FLKEY = 0xA5;     // Key Sequence 1
        FLKEY = 0xF1;     // Key Sequence 2
        VDM0CN = 0xA0;    // Enable VDD monitor and high threshold
        RSTSRC = 0x02;    // Enable VDD monitor as a reset source
        *pwrite = 0xAA;   // Write the byte
        PSCTL &= ~0x03;   // PSWE = 0 which disable writes

}

void FLASH_PageErase (void)
{
        unsigned char xdata * pwrite; // FLASH write pointer

        pwrite = (unsigned char xdata *) FLASH_WRITE_READ_ERASE;
        PSCTL = 0x03;    // PSWE = 1; PSEE = 1
        FLKEY = 0xA5;    // Key Sequence 1
        FLKEY = 0xF1;    // Key Sequence 2
        VDM0CN = 0xA0;   // Enable VDD monitor and high threshold
        RSTSRC = 0x02;   // Enable VDD monitor as a reset source
        *pwrite = 0;     // Initiate page erase
        PSCTL &= ~0x03;  // PSWE = 0; PSEE = 0
}

Thanks for your replies.

So far I have been able to erase a page and write a byte to that page; however, I have only been able to implement one function at the time, when I try to call both functions it seems that only the function that is called first is executed. I have included both of the functions to see if somebody can tell me why they are not executing when they are called one after the other.

Thanks

void FLASH_ByteWrite (void)
{
        unsigned char xdata * pwrite;           // FLASH write pointer

        pwrite = (unsigned char xdata *) FLASH_WRITE_READ_ERASE;
        PSCTL = 0x01;     // PSWE = 1 which enables writes
        FLKEY = 0xA5;     // Key Sequence 1
        FLKEY = 0xF1;     // Key Sequence 2
        VDM0CN = 0xA0;    // Enable VDD monitor and high threshold
        RSTSRC = 0x02;    // Enable VDD monitor as a reset source
        *pwrite = 0xAA;   // Write the byte
        PSCTL &= ~0x03;   // PSWE = 0 which disable writes

}

void FLASH_PageErase (void)
{
        unsigned char xdata * pwrite; // FLASH write pointer

        pwrite = (unsigned char xdata *) FLASH_WRITE_READ_ERASE;
        PSCTL = 0x03;    // PSWE = 1; PSEE = 1
        FLKEY = 0xA5;    // Key Sequence 1
        FLKEY = 0xF1;    // Key Sequence 2
        VDM0CN = 0xA0;   // Enable VDD monitor and high threshold
        RSTSRC = 0x02;   // Enable VDD monitor as a reset source
        *pwrite = 0;     // Initiate page erase
        PSCTL &= ~0x03;  // PSWE = 0; PSEE = 0
}

... waiting for erase complete before writing?

I tried putting different delays in between function calls but I'm still seeing the same problem. I am suspecting that I am getting an undesirable reset right after the erase but I haven't been able to figure out why this is happening.

UPDATE

I used an oscilloscope to trace how far my code was getting an I found out that the processor resets right after

 *pwrite = 0; // Initiate page erase

.

Does anybody has an idea why this is happening?

Thanks

Does anybody has an idea why this is happening?
yes, your puppy bites, disable the watchdog - unless you can set the timeout long enough.

I tried putting different delays in between function calls
does the chip you have not seen fit to reveale not have an "erase complete" flag. doing it with delays is not a good idea.

Since you have not revealed your chip, if it does not allow disabling the WD and you can not set a long enough time, you will need to run without it.

Erik