Supermicro SUPER P4SS8, User Manual

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