Appendix E: Post Code Diagnostic Led Decoder; Figure 63. Diagnostic Led Placement Diagram; Table 84. Post Progress Code Led Example - Intel BB5520UR Technical Product Specification

Intel® Server Boards S5520HC, S5500HCV and S5520HCT TPS

Appendix E: 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, you can use the Diagnostic LEDs to identify the last POST process 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 LED's #4, #5, #6, and #7. The lower nibble bits are represented by Diagnostics
LED's #0, #1, #2, and #3. If the bit is set in the upper and lower nibbles, the corresponding LED
lights up. If the bit is clear, the corresponding LED is off.
Diagnostic LED #7 is labeled "MSB" (Most Significant Bit), and Diagnostic LED #0 is labeled
"LSB" (Least Significant Bit).
A. Diagnostic LED #7 (MSB LED)
B. Diagnostic LED #6
C. Diagnostic LED #5
D. Diagnostic LED #4
In the following example, the BIOS sends a value of EDh to the diagnostic LED decoder. The
LED's are decoded as follows:
LED
LED's
#7
8h
Status
ON
1
Results
Revision 1.8

Figure 63. Diagnostic LED Placement Diagram

Table 84. POST Progress Code LED Example

Upper Nibble LED's
LED LED
#6 #5
4h 2h
ON ON
1 1
Eh
Intel order number E39529-013
Appendix E: POST Code Diagnostic LED Decoder
E. Diagnostic LED #3
F. Diagnostic LED #2
G. Diagnostic LED #1
H. Diagnostic LED #0 (LSB LED)
LED LED
#4 #3
1h 8h
ON ON
0 1
Lower Nibble LED's
LED LED
#2 #1
4h 2h
ON OFF
1 0
Dh
LED
#0
1h
ON
1
161