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Intel® Server D50DNP Family Integration and Service Guide
Appendix E. POST Code Diagnostic LEDs
To help troubleshooting system hang conditions that occur during a system POST process, the server board
includes a bank of eight diagnostic LEDs on the front edge of the board. These diagnostic LEDs are used
during POST to represent halt error codes or POST progress codes.
During the system boot process, memory reference code (MRC) and system BIOS execute several memory
initialization and platform configuration routines, each of which is assigned a hexadecimal POST progress
code number. As each routine is started, the given POST progress code number is displayed on the
diagnostic LEDs. If a system hangs during POST execution, the displayed POST progress code can be used to
identify the last POST routine that was run before the error occurred, helping to isolate the possible cause of
the hang condition even when video is not available.
These diagnostic LEDs are equivalent to the legacy "Port 80 POST codes", and a Legacy I/O Port 80 output
will be displayed as a Diagnostic LED code. Each POST progress code or halt error code is represented by
eight LEDs, four green LEDs and four amber LEDs. The codes are divided into two nibbles, an upper nibble
and a lower nibble. The upper nibble bits are represented by amber diagnostic LEDs and the lower nibble
bits are represented by green diagnostic LEDs. If the bit is set, the corresponding LED is lit. If the bit is clear,
the corresponding LED is off. For each set of nibble bits, LED with lowest number represents the least
significant bit (LSB) and LED with highest number represents the most significant bit (MSB).
Figure 266. Intel® Light-Guided Diagnostics - POST Code LED Location
In the following example, the BIOS sends a hexadecimal value of AC to the diagnostic LEDs. The LEDs are
decoded as shown in the following table.
Table 17. Diagnostic LED Code Example
Upper Nibble AMBER LEDs
Lower Nibble GREEN LEDs
MSB
LSB
LEDs
LED #7
LED #6
LED #5
LED #4
LED #3
LED #2
LED #1
LED #0
8h
4h
2h
1h
8h
4h
2h
1h
Status
ON
OFF
ON
OFF
ON
ON
OFF
OFF
Binary
1
0
1
0
1
1
0
0
Read
Value
Hexadecimal
Ah
Ch
Result
ACh
Upper nibble bits = 1010b = Ah; Lower nibble bits = 1100b = Ch; the two Hex Nibble values are combined to create a single ACh
POST Progress Code.
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