Appendix C. Post Code Diagnostic Led Decoder; Figure 28. Post Code Diagnostic Leds - Intel S1200SPL Technical Spesification

Intel® Server Board S1200SP Family Technical Product Specification
Appendix C. POST Code Diagnostic LED Decoder
As an aid to assist in trouble shooting a system hang that occurs during a system's Power-On Self - Test (POST)
process, the server board includes a bank of eight POST Code Diagnostic LEDs on the back edge of the server
board.
During the system boot process, Memory Reference Code (MRC) and System BIOS execute a number of
memory initialization and platform configuration processes, each of which is assigned a specific hex POST
code number. As each routine is started, the given POST code number is displayed to the POST Code
Diagnostic LEDs on the back edge of the server board.
During a POST system hang, the displayed post code can be used to identify the last POST routine that was
run prior to the error occurring, helping to isolate the possible cause of the hang condition.
Each POST code is represented by eight LEDs; four Green and four Amber. The POST codes are divided into
two nibbles, an upper nibble and a lower nibble. The upper nibble bits are represented by Amber Diagnostic
LEDs #4, #5, #6, #7. The lower nibble bits are represented by Green Diagnostics LEDs #0, #1, #2 and #3. If the
bit is set in the upper and lower nibbles, the corresponding LED is lit. If the bit is clear, the corresponding LED
is off.
Figure 29. POST Code Diagnostic LEDs
In the following example, the BIOS sends a value of ACh to the diagnostic LED decoder. The LEDs are decoded
as follows:
Note: Diag LEDs are best read and decoded when viewing the LEDs from the back of the system.
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