Appendix B: BIOS POST Checkpoint Codes

Appendix B

BIOS POST Checkpoint Codes

When AMIBIOS performs the Power On Self Test, it writes checkpoint codes to I/O port 0080h. If the computer cannot complete the boot process, diagnostic equipment can be attached to the computer to read I/O port 0080h.

B-1 Uncompressed Initialization Codes

The uncompressed initialization checkpoint codes are listed in order of execution:

Checkpoint

Code Description

D0h

The NMI is disabled. Power on delay is starting. Next, the initialization

 

code checksum will be verified.

D1h

Initializing the DMA controller, performing the keyboard controller

 

BAT test, starting memory refresh, and entering 4 GB flat mode next.

D3h

Starting memory sizing next.

D4h

Returning to real mode. Executing any OEM patches and setting the

 

Stack next.

D5h

Passing control to the uncompressed code in shadow RAM at

 

E000:0000h. The initialization code is copied to segment 0 and control

 

will be transferred to segment 0.

D6h

Control is in segment 0. Next, checking if <Ctrl> <Home> was pressed

 

and verifying the system BIOS checksum. If either <Ctrl> <Home>

 

was pressed or the system BIOS checksum is bad, next will go to

 

checkpoint code E0h. Otherwise, going to checkpoint code D7h.

B-1

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American Megatrends X6DVA-EG, X6DVA-4G user manual Uncompressed Initialization Codes, Checkpoint Code Description

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