Intel SR2600UR Service Guide - Page 177

Appendix C: 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 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 Table 7. POST Progress Code LED Example Upper Nibble LEDs MSB LED #7 LED #6 LED #5 LED #4 8h 4h 2h 1h ON OFF ON OFF LED #3 8h ON Lower Nibble LEDs LSB LED #2 LED #1 LED #0 4h 2h 1h ON OFF OFF 1 0 1 0 1 1 0 0 Ah Ch Intel® Server System SR2600UR/SR2625UR Service Guide 157