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Table 29
Miscellaneous Signal Descriptions
Signal
Pin # Description
I/O
PU/PD
Comment
SPKR
B32
Output for audio enunciator, the “speaker” in PC-AT systems
O 3.3V
WDT
B27
Output indicating that a watchdog time-out event has occurred.
O 3.3V
PD 10K
FAN_PWMOUT
B101
Fan speed control. Uses the Pulse Width Modulation (PWM) technique
to control the fan’s RPM.
O 3.3V
12V tolerant
FAN_TACHIN
B102
Fan tachometer input.
I
PU 47K 3.3V
Requires a fan with a two
pulse output. 12V tolerant.
TPM_PP
A96
Physical Presence pin of Trusted Platform Module (TPM). Active high.
I 3.3V
PD 10K
Note
For the correct fan control (FAN_PWMOUT, FAN_TACHIN) implementation, see the COM Express Design Guide.
Table 30
Power and System Management Signal Descriptions
Signal
Pin # Description
I/O
PU/PD
Comment
PWRBTN#
B12
Power button to bring system out of S5 (soft off), active on falling edge.
Note:
For proper detection, assert a pulse width of at least 16 ms.
I 3.3VSB
PU 10k 3.3VSB
SYS_RESET# B49
Reset button input. Active low input. Edge triggered.
System will not be held in hardware reset while this input is kept low.
Note:
For proper detection, assert a pulse width of at least 16 ms.
I 3.3VSB
PU 10k 3.3VSB
CB_RESET#
B50
Reset output from module to Carrier Board. Active low. Issued by module chipset and may result from
a low SYS_RESET# input, a low PWR_OK input, a main power input (VIN) that falls below the minimum
specification, a watchdog timeout, or may be initiated by the module software.
O 3.3VSB
PWR_OK
B24
Power OK from main power supply. A high value indicates that the power is good.
I 3.3V
PU 10k
SUS_STAT#
B18
Suspend Status: Indicates the system will enter a low power state soon. Used to notify LPC devices.
O 3.3VSB
SUS_S3#
A15
Indicates system is in Suspend to RAM state. Active-low output. An inverted copy of SUS_S3# on the
carrier board may be used to enable the non-standby power on a typical ATX power supply.
O 3.3VSB
SUS_S4#
A18
Indicates system is in Suspend to Disk (S4) or Soft Off (S5) state. Active low output.
O 3.3VSB
Same signal as
SUS_S5#
SUS_S5#
A24
Indicates system is in Soft Off state.
O 3.3VSB
Same signal as
SUS_S4#
WAKE0#
B66
PCI Express wake up request signal.
I 3.3VSB
PU 10k 3.3VSB
WAKE1#
B67
General purpose wake up signal. May be used to implement a wake-up request from an external device.
I 3.3VSB
PU 10k 3.3VSB
BATLOW#
A27
Battery low input. This signal may be driven low by external circuitry to signal that the system battery is low. I 3.3VSB
PU 10k 3.3VSB
LID#
A103
Lid button. Used by the ACPI operating system for a LID switch.
Note:
For proper detection, assert a pulse width of at least 16 ms.
I 3.3VSB
PU 47k 3.3VSB
SLEEP#
B103
Sleep button. Used by the ACPI operating system to bring the system to sleep state or to wake it up again.
Note:
For proper detection, assert a pulse width of at least 16 ms.
I 3.3VSB
PU 47k 3.3VSB
