B-1
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 initializa-
tion code checksum will be verifi ed.
D1h
Initializing the DMA controller, performing the keyboard controller
BAT test, starting memory refresh, and entering 4 GB fl at 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 checkpoicode
D7h.
