Intel S3420GPLC Product Specification - Page 131

Intel® Server Board S3420GP TPS Appendix C: POST Code Diagnostic LED Decoder 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". Figure 43. 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 74. POST Progress Code LED Example LEDs MSB LED #7 8h Upper Nibble LEDs LED #6 4h LED #5 2h LED #4 1h LED #3 8h Lower Nibble LEDs LED #2 4h LED #1 2h LSB LED #0 1h Status ON OFF ON OFF ON OFF ON OFF Results 1 0 1 Ah 0 1 1 0 Ch 0  Upper nibble bits = 1010b = Ah; Lower nibble bits = 1100b = Ch; the two are concatenated as ACh. Revision 2.4 119 Intel order number E65697-010