Appendix C: Post Code Diagnostic Led Decoder; Figure 43. Diagnostic Led Placement Diagram; Table 74. Post Progress Code Led Example - Intel S3420GPLC - Server Board Motherboard Specification

Intel® Server Board S3420GP TPS

Appendix C: 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, 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", 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:
MSB
LEDs
LED #7
8h
Status ON
1
Results
Upper nibble bits = 1010b = Ah; Lower nibble bits = 1100b = Ch; the two are

concatenated as ACh.
Revision 2.4

Figure 43. Diagnostic LED Placement Diagram

Table 74. POST Progress Code LED Example

Upper Nibble LEDs
LED #6 LED #5
4h 2h
OFF ON
0 1
Ah
Intel order number E65697-010
Appendix C: POST Code Diagnostic LED Decoder
LED #4 LED #3
1h 8h
OFF ON
0 1
Lower Nibble LEDs
LED #2 LED #1
4h 2h
OFF ON
1 0
Ch
LSB
LED #0
1h
OFF
0
119