Technical Product Specification

Appendix B: POST Code LED Decoder Intel® Server System SR1690WB TPS
Revision 1.7
Intel order number: E72797-009
52
Appendix B: POST Code 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, you can use the diagnostic LEDs to identify the last POST
process 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” (Most Significant Bit), and the diagnostic LED #0
is labeled as “LSB” (Least Significant Bit).
Figure 28. 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 52. 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.