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4.2 Port 80h POST Codes
During the POST, the BIOS generates diagnostic progress codes (POST-codes) to I/O port 80h. If
the POST fails, execution stops and the last POST code generated is left at port 80h. This code is
useful for determining the point where an error occurred.
Displaying the POST-codes requires a PCI bus add-in card, often called a POST card. The POST
card can decode the port and display the contents on a medium such as a seven-segment display.
NOTE
The POST card must be installed in PCI bus connector 1.
The tables below offer descriptions of the POST codes generated by the BIOS. Table 49 defines
the uncompressed INIT code checkpoints, Table 50 describes the boot block recovery code
checkpoints, and Table 51 lists the runtime code uncompressed in F000 shadow RAM. Some codes
are repeated in the tables because that code applies to more than one operation.
Table 49.
Uncompressed INIT Code Checkpoints
Code
Description of POST Operation
D0
NMI is Disabled. Onboard KBC, RTC enabled (if present). Init code Checksum verification
starting.
D1
Keyboard controller BAT test, CPU ID saved, and going to 4 GB flat mode.
D3
Do necessary chipset initialization, start memory refresh, and do memory sizing.
D4
Verify base memory.
D5
Init code to be copied to segment 0 and control to be transferred to segment 0.
D6
Control is in segment 0. To check recovery mode and verify main BIOS checksum. If either it is
recovery mode or main BIOS checksum is bad, go to check point E0 for recovery else go to check
point D7 for giving control to main BIOS.
D7
Find Main BIOS module in ROM image.
D8
Uncompress the main BIOS module.
D9
Copy main BIOS image to F000 shadow RAM and give control to main BIOS in F000
shadow RAM.
Table 50.
Boot Block Recovery Code Checkpoints
Code
Description of POST Operation
E0
Onboard Floppy Controller (if any) is initialized. Compressed recovery code is uncompressed in
F000:0000 in Shadow RAM and give control to recovery code in F000 Shadow RAM. Initialize
interrupt vector tables, initialize system timer, initialize DMA controller and interrupt controller.
E8
Initialize extra (Intel Recovery) Module.
E9
Initialize floppy drive.
EA
Try to boot from floppy. If reading of boot sector is successful, give control to boot sector code.
EB
Booting from floppy failed, look for ATAPI (LS-120, Zip) devices.
EC
Try to boot from ATAPI. If reading of boot sector is successful, give control to boot sector code.
EF
Booting from floppy and ATAPI device failed. Give two beeps. Retry the booting procedure again
(go to check point E9).
Error Messages and Beep Codes
77
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