Hi buddy. I am designing for 8051 memory extened version with VHDL.
According to the reference in P89C669(Philips 8051 Memory extended version), EPTR has 23bit width and P89C669 ignores MSB(24th bit). so it can address 23bit and access 8MB memory. but I'd like to design that microcontroller that can address 24bit and access 16MB DATA and Code memory respectively. at this point, I wonder if I can use the MSB(24th bit of EPTR). in other words, the compiler can recognize 24bit EPTR?
(sorry for poor Eng..)
The problem with this is that the compiler would actually need to understand 25-bit (really 32-bit pointers) to do what you want.
The reason for this is that a generic pointer SHOULD be able to access all memory space. So, if you have 24-bit addresses for DATA and 24-bit addresses for CODE, and if CODE and DATA are separate, then you need 25-bits to access it all.
That's the reason Philips implemented 23-bit pointers for CODE and DATA.
Jon