Appendix C: Led Decoder; Figure 53. Diagnostic Led Placement Diagram; Table 9. Post Progress Code Led Example - Intel SR1690WB - Server System - 0 MB RAM Service Manual

Appendix C: 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 the 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, #7. The lower nibble bits are represented by
Diagnostics LEDs #0, #1, #2 and #3. Given the bit is set in the upper and lower nibbles,
then corresponding LED is lit. If the bit is clear, corresponding LED is off.
The Diagnostic LED #7 is labeled as "MSB", and the Diagnostic LED #0 is labeled with
"LSB".
POST LED 7
POST LED 6
POST LED 5
POST LED 4

Figure 53. Diagnostic LED Placement Diagram

Table 9. POST Progress Code LED Example

Upper Nibble LEDs
MSB
LEDs
LED LED
#7 #6
POST LED 0
POST LED 1
POST LED 2
POST LED 3
Lower Nibble LEDs
LED LED LED
#5 #4 #3
AF003321
LSB
LED LED LED
#2 #1 #0
73