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Table 26: ATX Signal Names
ATX Signal Name
Description
Active-low, TTL-level input to ATX supply that, when low, enables all power rails. If high or
PS_ON#
floating, all ATX power rails are disabled except for the +5V Suspend rail.
PWR_OK
Active-high, TTL-level output signal from the ATX supply that indicates that the +12V, +5V,
+3.3V and -12V outputs are all present and OK to use.
+12V1DC
+12V power rail for use by all system components except for the CPU, controlled by
+12V power rail for use by the CPU, controlled by PS_ON#. This power rail
+12V2DC
appears on a separate 2x2 connector for CPU use only.
+5VDC
+5V power rail, controlled by PS_ON#
+3.3VDC
+3.3V power rail, controlled by PS_ON#
-12VDC
-12V power rail, controlled by PS_ON#
+5V Suspend power rail, present whenever the ATX supply is connected to its AC
+5VSB
power input source.
COM
Common return path – usually referred to as "ground" or GND.
76
COM Express® Carrier Board Design Guide
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