RM23712 TPS
83
Appendix B: 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-est (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 groups, 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 54. POST Diagnostic LED Location
In the following example, the BIOS sends a value of ACh to the diagnostic LED decoder.
The LEDs are decoded as follows:
Table 54.POST Progress Code LED Example
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