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POST Code Checkpoints
Each of the four LEDs can have one of four states: Off, Green, Red, or
Amber. The LED diagnostics feature consists of a hardware decoder
and four dual color LEDs. During POST, the LEDs will display all normal
Port80 codes representing the progress of the BIOS POST. Each
postcode will be represented by a combination of colors from the 4
LEDs. During the POST process, each light sequence represents a
specific Port-80 POST code. If a system should hang during POST, the
Diagnostic LEDs will present the last test executed before the hang.
When reading the lights, the LEDs should be observed from the back of
the system.
Check
point
Diagnostic LED Decoder
DescriptionG=Green, R=Red, A+Amber
MSB LSB
03 OFF OFF G G Disable NMI, parity, video
for EGA, and 03DMA
controllers. Initialize BIOS,
POST, Run-time data area.
Initialize BIOS modules on
POST entry and GPNV
area. Initialized CMOS as
mentioned in the Kernel
Variable “wCMOSFlags”
04 OFF G OFF OFF Check CMOS diagnostic
byte to determine if
battery power is OK and
CMOS checksum is OK.
Verify CMOS checksum
manually by reading
storage area. If the CMOS
checksum is bad, update
CMOS with power-on
default values and clear
passwords. Initialize status
register A.
Initializes data variables
that are based on CMOS
setup questions. Initializes
both the 8259 compatible
PICs in the system
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