Technical Product Specification

Appendix D: POST Code Diagnostic LED Decoder Intel® Server Boards S4600LH2/T2 TPS
Revision 2.0
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Appendix D: 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 58. Post Code LED location