Kontron COMe Starterkit Eval T2 - Manual (Page 135)

COM Express Interfaces
2.22.4. Power Management Signals
COM Express specifies a set of signals to control the system power states such as the power-on
and reset conditions. This enables the system designer to implement a fully ACPI compliant
system supporting system states from S0 to S5. The minimum hardware requirements for an
ACPI compliant system are an ATX conforming power supply and a power button.
The following table provides a short description of the ACPI defined system states S0 to S5
including the corresponding power rail state. For more information about ACPI and the several
system power states, refer to the 'Advanced Configuration and Power Interface Specification
Revision'.
Table 44: System States S0-S5 Definitions
System State Description Power Rail State
S0
Full On All components are powered and the system is fully
functional. Full power on all power rails.
S1
Power-on Standby
(POS) In sleeping state, no system context is lost, hardware
maintains all system context. During S1 operation some
system components are set into low power state. Full power on all power rails.
S2 Not supported.
S3
Suspend to RAM (STR) The current system state and context is stored in main
memory and all unnecessary system logic is turned off. Only main memory and logic required
to wake-up the system remain
powered by the Suspend voltages. All
other power rails are switched off.
S4
Suspend to Disk (STD)
Hibernate The current system state and context is stored on disk and
all unnecessary system logic is turned off. S4 is similar to
S5 and just supported by OS. Similar to S5; All other power rails are
switched off.
S5
Soft Off In S5 state the system is switched off. Restart is only
possible with the power button or by a system wake-up
event such as 'Wake On LAN' or RTC alarm. Suspend power rails are powered. All
other power rails are switched off.
Table 45: Power Management Signal Descriptions
Signal Pin Description I/O Comment
PWRBTN# B12 Power button low active signal used to wake up the
system from S5 state (soft off). This signal is
triggered on the falling edge. I 3.3V Suspend
CMOS Drive with >=10mA
SYS_RESET# B49 Reset button input. Active low request for Module to
reset and reboot. May be falling edge sensitive. For
situations when SYS_RESET# is not able to
reestablish control of the system, PWR_OK or a
power cycle may be used. I 3.3V Suspend
CMOS Drive with >=10mA
CB_RESET# B50 Reset output signal from Module to Carrier Board.
This signal may be driven low by the Module to reset
external components located on the Carrier Board. O 3.3V Suspend
CMOS
PWR_OK B24 Power OK status signal generated by the ATX power
supply to notify the Module that the DC operating
voltages are within the ranges required for proper
operation. I 3.3V
CMOS
SUS_STAT# B18 Suspend status signal to indicate that the system will
be entering a low power state soon. It can be used
by other peripherals on the Carrier Board as an
indication that they should go into power-down mode. O 3.3V
Suspend
CMOS
SUS_S3# A15 S3 Sleep control signal indicating that the system
resides in S3 state (Suspend to RAM). O 3.3V
Suspend
CMOS This signal can be used
to control the ATX
power supply via the
'PS_ON#' signal.
SUS_S4# A18 S4 Sleep control signal indicating that the system
resides in S4 state (Suspend to Disk). O 3.3V
Suspend
CMOS
PICMG ® COM Express ® Carrier Board Design Guide Rev. 2.0 / December 6, 2013
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