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> DOS > Debugging ROM BIOS / register offsets |
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vid 21 Feb 2004, 11:39
mov byte al,[f000:0]
"f000" is not a number, it starts with letter so it is symbol. use 0F000h or 0xF000 or $F000. you want to grab BIOS's code and play with it? |
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21 Feb 2004, 11:39 |
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Bitdog 21 Feb 2004, 17:36
MOV AX, BYTE PTR [F000]
seg over rides consist of the seg before the instruction But you can't put a seg reg infront. Seg regs CS, DS, ES, etc have a value, and that value is placed before DB 66 MOV AX, BYTE PTR [F000] or something like that, you'll want the value of DS seg reg, so assemble a blank.asm to .com that has two lines of code in it. MOV BYTE [100h],5 MOV BYTE [DS:100h],5 then run it through a debugger and you'll see the machine code value for DS or any other seg reg. Then use that in debug.exe as a pre instruction seg over ride. Debug.exe works as a disassembler, and from it's output you can learn how to use it as an assembler. I have a debug disassembler for you.... http://bitdog.home.att.net/files/fasmenv.zip look for the DISBUG dir DISBUG MY.COM 45 disassembles a 45 byte .com file named MY.COM it makes assemble batch files and two source .asm files. .BUG & .DAT ? It comes with its Fasm .asm source code. I hope it helps somehow Bitdog |
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21 Feb 2004, 17:36 |
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vid 21 Feb 2004, 19:10
, yes, sorry. It so long from when i was working with segments last time...
but you must use *h/0x*/$* anyway. so it would be somethink like Code: mov ax,0F000h mov dx,ax mov al,[ds:1] |
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21 Feb 2004, 19:10 |
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