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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.
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.
Appendix B: BIOS POST Checkpoint Codes
Appendix B
B-1
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