over 16 bit DPTR limit

The Keil tools support extended DPTRs by using far memory. You'll have to customize XBANKING.A51 or L51_BANK.A51 to support your exact hardware.

The 8051 variants I know with extended DPTRs have 24-bit DPTRs -- one additional byte per pointer. The Keil generic/far pointer scheme is also a 3-byte format, so it can't store 32-bit addresses.

If you really need 32-bit-wide DPTRs, you're going to have to do most of the work yourself. Create a type that is 32 bits (a structure, as you suggest). Then you'll need to create some library routines to write the upper bits of that value to your extended hardware, and the lower bits to the DPTR proper. You'll probably want routines to set a memory bank and to extract a far pointer from the 32-bit value.

The Keil tools support extended DPTRs by using far memory. You'll have to customize XBANKING.A51 or L51_BANK.A51 to support your exact hardware.

The 8051 variants I know with extended DPTRs have 24-bit DPTRs -- one additional byte per pointer. The Keil generic/far pointer scheme is also a 3-byte format, so it can't store 32-bit addresses.

If you really need 32-bit-wide DPTRs, you're going to have to do most of the work yourself. Create a type that is 32 bits (a structure, as you suggest). Then you'll need to create some library routines to write the upper bits of that value to your extended hardware, and the lower bits to the DPTR proper. You'll probably want routines to set a memory bank and to extract a far pointer from the 32-bit value.

Thanks, so at the end my solution is:

typedef union U32
{
        unsigned long dword;
        unsigned short word[2];
        unsigned char byte[4];
} bdata U32;
...
unsigned long Inc32bitDPTR (unsigned long addr)
{
        U32 idata tmp_dptr;

        tmp_dptr.dword = addr;
        tmp_dptr.dword++;
        switch (DPS)
        {
                case 0x00:
                        DPL0 = tmp_dptr.byte[3];
                        DPH0 = tmp_dptr.byte[2];
                        break;
                case 0x01:
                        DPL1 = tmp_dptr.byte[3];
                        DPH1 = tmp_dptr.byte[2];
        }

        if (tmp_dptr.dword >= MAX_ADDR)
                tmp_dptr.dword = 0;

        return tmp_dptr.dword;
}
...
tmp_dptr_dst.dword = addr;//long addr;
WriteByte (tmp_dptr_dst.dword, byte);
tmp_dptr_dst.dword = Inc32bitDPTR(tmp_dptr_dst.dword);
...

May be anybody realized it better and faster?

I would avoid the use of "word" to mean "16 bits"

See: www.8052.com/.../read.phtml

Strictly, on an 8051, the word-size is 8 bits.

I would avoid the use of "word" to mean "16 bits"

Micro$oft wouldn't :)

They currently uses it to mean half (and possibly also a quarter of) the size of an integer register...)

That's because they used it specifically in the context of their original 16-bit platform.

They are now stuck with it for 32- and 64-bit platforms.

Serves 'em right!

Learn form their mistake!