bios reset in dos?

[Ben3D]

Okay, I have a simple piece of assembly code...now I want to jump to the bios reset area and reset the pc to a cold restart if that makes sense.

I think memory location 0472 should be 1234h, and the bios offset is at FFFF0h...

So how would I perform a reset in asm...only new to assembly...but its in a different segment so its sort of complicated.

Thanx for any help..

(i'm using the masm assembler)

 

[boz78]

To reset PC you can use INT 19h...

 

[Ben3D]

yup...but I want to do it the other way..... I'm just learning to master asm, and wanted to see how you do it this way, instead of using int 19

 

[Ben3D]

now I have a masm assembler...but how come this line gives me an error:

jmp far 0100:0000

As this will allow me to change CS and IP...but I get the error:

"Left operand must have segment"

Thanks for any help on this

Ben

 

[AirCon]

IIRC it would be like this:

mov	ax, 40h
mov	ds, ax
mov	bx, 72h
mov	word ptr [bx], 1234h

mov	ax, 0FFFFh
push	ax
xor	ax,ax
push	ax
retf

Good luck

 

[Ben3D]

Thanx AirCon,
thats fantastic...thats just what I wanted to know how to do....

Brilliant....couldn't work out how to do that for ages...but you've solved my problem

Thanx again AirCon.


Ben

 

[AirCon]

Yes it is DOS-only. Windows works differently. You have to know what is the limitation in windows

 

[straiph]

the retf seems a bit long winded to me

when ever i want to perform a hard coded far jump i always use the following

this is 16bit code so the address after the opcode is a word and not a dword.

my ASM code would look something like:

db 0EAh ;Opcode for JMP FAR Immediate
dw 0h,0FFFFh

personally i use it all the time because the assemblers wont let me do it conventionally. but its alot shorter than friging the stack for a retf.

straiph



"There are 10 types of people in this world, those who know binary and those who don't!"

 

[AirCon]

Hi adholioshake,
Windows disables the bios routine. Instead you could use the Windows API function 'ExitWindowsEx(...)'