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Chapter 10 Solving Problems
POST Codes and Countdown Codes
The BIOS indicates the current testing phase during POST after the video
adapter has been successfully initialized by outputting a 2-digit hex code to
I/O location 80h. If a port-80h ISA card is installed, it displays this 2-digit
code on a pair of hex display LEDs.
Normal Port-80 Codes
These are the port-80 codes and countdown codes displayed during the
normal BIOS POST process.
Table 10-2. Port-80 Codes
Port 80 Code Reason
02 Verify Real Mode
04 Get CPU type
06 Initialize system hardware
08 Initialize chipset registers with initial POST values
09 Set in POST flag
0A Initialize CPU registers
0B Enable CPU cache
0C Initialize caches to initial POST values
0E Initialize I/O
0F Initialize the local bus IDE
10 Initialize Power Management
11 Load alternate registers with initial POST values new
12 Restore CPU control word during warm boot
14 Initialize keyboard controller
16 BIOS ROM checksum
Continued