Technical Product Specification

Appendix B: POST Code Diagnostic LED Decoder Intel®

Server System SR1625UR TPS

84 Intel order number E47487-012 Revision 2.0

Appendix B: POST Code Diagnostic LED Decoder

During the system boot process, the 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, the BIOS displays the POST code to the POST Code Diagnostic LEDs 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 that was executed.

Each POST code is represented by eight amber Diagnostic LEDs. The POST codes are divided

into two nibbles, an upper nibble and a lower nibble. The upper nibble bits are represented by

Diagnostic LEDs #4, #5, #6, and #7. The lower nibble bits are represented by 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.

The Diagnostic LED #7 is labeled as “MSB”, and the Diagnostic LED #0 is labeled as “LSB”.

A. Status LED

B. ID LED

C. Diagnostic LEDs

Figure 47. Diagnostic LED Placement Diagram

In the following example, the BIOS sends a value of ACh to the diagnostic LED decoder. The

LEDs are decoded as follows:

Table 64. POST Progress Code LED Example

LEDs

Upper Nibble LEDs

Lower Nibble LEDs

MSB

LSB

LED #7

LED #6

LED #5

LED #4

LED #3

LED #2

LED #1

LED #0

Status

OFF

Results

 Upper nibble bits = 1010b = Ah; Lower nibble bits = 1100b = Ch; the two are

concatenated as ACh.