writing to screen using register to define effective adrress

[suthers]

When i use the following code to write to the screen:

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mov bx, 0B8140h    
mov byte [ds:bx], 'T'
add bx, 1     
mov byte [ds:bx], 1Bh

It assembles with the warning: word value exceeds bounds.
What would be a suitable alternative that would allow it to work.
Thanks in advance,
Jules

[jerryleecooper]

YOu are putting more data in bx than it can contain. It's no time for the omega point yet.
put 0xb814 into ds and 0 into bx.
segment addresses are << 4 to the other addresses.
Sorry for my poor english, English, I mean.

[pcmattman]

Assuming real mode and therefore real mode segment interpretation:

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push ds
mov ds,0b800h
mov bx, 0140h
mov byte [ds:bx], 'T'
add bx, 1
mov byte [ds:bx], 1Bh
pop ds

Linear = seg << 4 + offset.

In Pmode, you can just use eax .

Edit: Added pop ds to the code snippet.

[suthers]

Yah, I should of said that i was in protected mode.
Thanks i just used eax to store the address
Jules

[jal]

[quote="pcmattman"]

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mov ds,0b800h

This should of course be

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mov ax, 0b800h
mov ds, ax

as mov ds does not take an immediate values as operand.


JAL

[Dex]

You could also use

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mov   byte [ds:0xB8140], "T"
mov   byte [ds:0xB8141], 1Bh

[pcmattman]

jal: True, but I didn't want to just give away the answer as easily as that .