video memory addressing

[wannabedeveloper]

Okay, just a quick question. How would you go about writing to an address like a000:013f? I've tried various things like a000:[013f] but none seem to work?

[JackScott]

Firstly, what language are you trying to use?
Secondly, can you show us the code that isn't working?
Thirdly, what about it isn't working?

[a5498828]

question is how would i write? wtf. i would use for eg. mov/movs/stos, or a bios function.

this is address of a graphic mode of video controller. Have you set it go graphic mode? Maybe you dont see pixel. TRy reading it back.

Have you set cache to uc/wc/wt? if its wb it wont work well, and wp you wont read correct data but pixel wil lstill display correctly.

[Solar]

How would you go about writing to an address like a000:013f?

That's a real mode address. I.e., the 0xa000 must be loaded to a segment register, and the actual access be offset by the 0x013f.

Code: Select all

Mov BX, a000h
Mov ES, BX
Mov BX, 013fh
Mov AL, [ES:BX] 

Of course, things are different in protected mode.

[Gigasoft]

Code: Select all

push 0a000h
pop es
mov byte ptr es:[13fh],whatever

[Chandra]

How would you go about writing to an address like a000:013f?

That's a real mode address. I.e., the 0xa000 must be loaded to a sector register, and the actual access be offset by the 0x013f.

Code: Select all

Mov BX, a000h
Mov ES, BX
Mov BX, 013fh
Mov AL, [ES:BX] 

Of course, things are different in protected mode.

It's not 'sector register' but a 'segment register'. Anyway, well done Solar.