Technical Product Specification

Table Of Contents
Appendix B: POST Code Diagnostic LED Decoder Intel
®
Server Board S5400SF TPS
Revision 2.02
Intel order number: D92944-007
158
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 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 is 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 following example, the 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 92: 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
AF002181
BIT 2
LSB
BIT 3
MSB
Diagnostic LEDs
Figure 54. Diagnostic LED Placement Diagram