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Appendix C:
During the system boot process, the BIOS executes a number of platform configuration
processes, each of which is assigned a specific hex POST code number. As each
configuration routine is started, the BIOS displays the POST code to the POST Code
Diagnostic LEDs found on the back edge of the server board. To assist in troubleshooting
a system hang during the POST process, the Diagnostic LEDs can be used to identify the
last POST process to be executed.
Each POST code is represented by the eight amber Diagnostic LEDs. The POST codes are
divided into two nibbles, an upper nibble and a lower nibble. The upper nibble bits are
represented by Diagnostic LEDs #4, #5, #6, #7. The lower nibble bits are represented by
Diagnostics LEDs #0, #1, #2 and #3. If the bit is set in the upper and lower nibbles, then
the corresponding LED is lit. If the bit is clear, then the corresponding LED is off.
The Diagnostic LED #7 is labeled as "MSB", and the Diagnostic LED #0 is labeled as
"LSB".
In the following example, the BIOS sends a value of ACh to the diagnostic LED decoder.
The LEDs are decoded as follows:
•
"Upper nibble bits = 1010b = Ah;
•
Lower nibble bits = 1100b = Ch;
The two are concatenated as ACh
LEDs
Status
Result
®
Intel
Server System SR2600UR/SR2625UR Service Guide
LED Decoder
Table 8. POST Progress Code LED Example
Upper Nibble LEDs
MSB
LED #7
LED #6
LED #5
8h
4h
2h
ON
OFF
ON
1
0
Ah
LED #4
LED #3
1h
8h
OFF
ON
1
0
1
Lower Nibble LEDs
LED #2
LED #1
LED #0
4h
2h
ON
OFF
1
0
Ch
LSB
1h
OFF
0
153
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