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. |
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