Appendix F: POST Code Diagnostic LED Decoder Intel® Server Board S2600CO Family TPS
Revision 1.4
Intel order number G42278-004
140
Appendix F: POST Code Diagnostic LED Decoder
As an aid to assist in troubleshooting 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 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, and #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, 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:
Note: Diagnostic LEDs are best read and decoded when viewing the LEDs from the back of the
system
Table 75. POST Progress Code LED Example
LEDs
Upper Nibble AMBER LEDs Lower Nibble GREEN LEDs
MSB LSB
LED #7 LED #6 LED #5
LED #4
LED #3
LED #2
LED #1 LED #0
8h 4h 2h 1h 8h 4h 2h 1h
Status
ON OFF ON OFF ON ON OFF OFF
Results
1 0 1 0 1 1 0 0
Ah Ch
Upper nibble bits = 1010b = Ah; Lower nibble bits = 1100b = Ch; the two are
concatenated as ACh.
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