IBM CMX58886CX user manual AT vs. ATX Power Supplies, ATX Power Supply Signals

•Resume on RTC Alarm: The RTC Alarm allows the system to turn on at a certain time every day. This option is BIOS configurable.

AT vs. ATX Power Supplies

Both AT and ATX power supplies may be used with the CMX58886CX cpuModule, however AT power supplies do not provide any standby power to the cpuModule. When an AT power supply is used to power the system, low power modes that require a standby power to wake the system will not be fully supported.

ATX power supplies do provide a standby power, thus allowing the system to utilize all low power modes supported by the hardware. When an ATX supply is used to power the cpuModule, lower power modes can be acheived. During these low power modes, the standby power from the ATX power supply provides power to a small circuit on the CPU, which is used to watch for a system wake event.

ATX Power Supply Signals

The auxiliary power connector (CN3) provides two ATX style signals., +5V Standby and PSON#. The +5V Standby rail is used to power certain parts of the cpuModule when the main power supply is turned off, i.e. during Suspend-to-RAM (S3), Hibernate (S4), or Soft-Off (S5) power modes. The PSON# signal is an active low open-drain ouput that signals the power supply to turn on. Use of these signals allows the power consumption to drop to below 1W during standby modes, and still enable any of the wake events.

The CPU monitors power supply inputs, and also generates the ATX Power Good signal.

BDM-610000050 Rev A Chapter 4: Using the cpuModule 67