Technical Product Specification

Appendix D: POST Code Diagnostic LED Decoder Intel® Server Board S5520UR and S5520URT TPS
Intel order number E44031-012 Revision 1.9
150
Appendix D: POST Code Diagnostic LED Decoder
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 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 that was 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, and #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”.
A. Status LED
B. ID LED
C. Diagnostic LEDs
Figure 49. Diagnostic LED Placement Diagram
In the following example, the BIOS sends a value of ACh to the diagnostic LED decoder. The
LEDs are decoded as follows:
Table 87. POST Progress Code LED Example
LEDs
Upper Nibble LEDs
Lower Nibble LEDs
MSB
LSB
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
Results
1
0
1
0
1
1
0
0
Ah
Ch
 Upper nibble bits = 1010b = Ah; Lower nibble bits = 1100b = Ch; the two are
concatenated as ACh.