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Appendix B: POST Code Diagnostic LED Decoder Intel® Server System SR2500AL
Revision – 1.6
Intel order number D31980-009
92
Appendix B: POST Code Diagnostic LED Decoder
During the system boot process, 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, BIOS will display the given 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 will be represented by a combination of colors from the four LEDs. The LEDs
are capable of displaying three colors: green, red, and amber. The POST codes are divided into
two nibbles, an upper nibble and a lower nibble. Each bit in the upper nibble is represented by a
red LED and each bit in the lower nibble is represented by a green LED. If both bits are set in
the upper and lower nibbles then both red and green LEDs are lit, resulting in an amber color. If
both bits are clear, then the LED is off.
In the below example, BIOS sends a value of ACh to the diagnostic LED decoder. The LEDs
are decoded as follows:
•
red bits = 1010b = Ah
•
green bits = 1100b = Ch
Since the red bits correspond to the upper nibble and the green bits correspond to the lower
nibble, the two are concatenated to be ACh.
Table 56: POST Progress Code LED Example
8h 4h 2h 1h
LEDs Red Green Red Green Red Green Red Green
ACh 1 1 0 1 1 0 0 0
Result Amber Green Red Off
MSB LSB
Figure 53. Diagnostic LED Placement Diagram
LSB MSB
Diagnostic LEDs
Back edge of baseboard
USB Port
USB Port