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Joined: 21 May 2010
Posts: 287
eeprom is not writeable, right?
when i want to modify its contents, i need external hardware to do that.

is it possible to destroy bios by writing to its memory? or write operation wont have any effect?
Post 31 Jul 2010, 17:54
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Joined: 20 Feb 2006
Posts: 4237
Location: 2018
the rom of the bios can be erased if it is a model made for that, and if it is erasable, it is rewritable too. then, if you have an eeprom programmer, you just have to test after reading of the datasheet.
Post 31 Jul 2010, 18:50
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Your code has a bug

Joined: 06 May 2005
Posts: 4633
Location: Argentina
If your question is whether multiple garbage writes to F0000-FFFFF will cause any harm to the memory the answer is no, but external hardware may not be needed neither if the motherboard support flashing (but if it supports there is no common method that allows flashing on all motherboards).

Also, I think I read somewhere that some motherboards accepts digitally signed binaries only. If this is true the validation is probably in hardware or perhaps you can load a new BIOS from the boot up sequence only and once that stage is passed the memory is programmed to be locked until next reset.
Post 31 Jul 2010, 18:59
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DJ Mauretto

Joined: 14 Mar 2007
Posts: 464
Location: Rome,Italy
DJ Mauretto
Hello Very Happy
Usually you can retrive Manufacturer and Model of your FWH
( Firmware Hub or flash eeprom) in different ways.
This is true for some FWH:

     MOV     ESI,0FFBC0000H          ; JEDEC Boot Device Register
        MOV     AL,[ESI]                        ; Read Manufacturer ID
      MOV     BL,[ESI+1]                 ; Read Model ID


There are some flash eeprom that request a key:
   MOV     AL,0AAH
     MOV     ESI,0FFFF5555H
      MOV     [ESI],AL

        MOV     AL,55H
      MOV     ESI,0FFFF2AAAH
      MOV     [ESI],AL

        MOV     AL,90H
      MOV     ESI,0FFFF5555H
      MOV     [ESI],AL

        MOV     ESI,0FFFF0000H
      MOV     AL,[ESI]                ; Manufacturer ID
   MOV     BL,[ESI+1]              ; ModeL ID

The famous Intel 82802 FWH:
    MOV     ESI,0FFFF0000H          ; Intel Firmware Hubs Address
       MOV     AL,-1                            ; AL = Command - Reset/Read Array
  MOV     [ESI],AL

        MOV     AL,90H                  ; AL = Command - Read Identifier Codes
      MOV     [ESI],AL
    MOV     AL,[ESI]                        ; AL = Manufacturer Code (89H)
      MOV     BL,[ESI+1]                      ; BL = Device Code       (4Mbit = ADH, 8Mbit = ACH)

Then you need of datasheet of your chip to write your BIOS in to the chip
without external component, usually in Real Mode and Have fun with 'b1528932' Bios v1.0 Wink

Nil Volentibus Arduum Razz
Post 02 Aug 2010, 12:02
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Joined: 19 Nov 2009
Posts: 1216
Location: NC, USA
CPU Wizard -> Mainboard -> BIOS -> Flashable will tell you if your BIOS is writable. It just won't tell you how. Razz
Post 03 Aug 2010, 00:16
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