NXP Semiconductors
FXTH87E
FXTH87E, Family of Tire Pressure Monitor Sensors
FXTH87ERM
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Reference manual
Rev. 5.0 — 4 February 2019
109 / 183
period of the resulting interrupt also generates the clock, RCLK, for the periodic reset
timing.
Table 99. PWU Control/Status register 0 (PWUCS0) (address $0039)
Bit
7
6
5
4
3
2
1
0
R
0
W
WUF
WUFAK
WUT[5:0]
Reset
0
—
1
1
1
1
1
1
Table 100. PWUSC0 register field descriptions
Field
Description
7
WUF
Wakeup Interrupt Flag — The WUF bit indicates when a wakeup interrupt has been generated by the PWU.
This bit is cleared
by writing a one to the WUFAK bit. Writing a zero to this bit has no effect. Reset clears this bit.
0 Wakeup interrupt not generated or was previously acknowledged.
1 Wakeup interrupt generated.
6
WUFAK
Acknowledge WUF Interrupt Flag — The WUFAK bit clears the WUF bit if written with a one. Writing a zero
to the WUFAK bit has no effect on the WUF bit. Reading the WUFAK bit returns a zero. Reset has no effect
on this bit.
0 No effect.
1 Clear WUF bit.
5:0
WUT[5:0]
WUF Time Interval — These control bits select the number of WCLK clocks that are needed before the next
wakeup interrupt is generated. The count gives a range of wakeup times from 1 to 63 WCLK clocks.
Depending on the value of the bits for the WDIV[5:0] this time interval can nominally be from 1 to 63
seconds in 1 second steps.
Whenever the WUT[5:0] bits are changed the timeout period is restarted. Writing the same data to the
WUT[5:0] bits has no effect.
Writing zeros to all of the WUT[5:0] bits forces the wakeup divider to a value of $3F and disables the
wakeup interrupt. However,
writing all zeros to the WUT[5:0] bits is inhibited if all of the PRST[5:0] bits are already cleared to zero. This
prevents disabling both the periodic wakeup and the periodic reset at the same time. See
Table 101
.
The WUT[5:0] bits are preset to a value of $3F (decimal 63) by any resets.
Table 101. Limitations on clearing WUT/PRST
Control Bits
State of Control
Bits
Control Bits to
be Cleared
Resulting
Action
Resulting
Wakeup
Interrupt
Resulting
Periodic Reset
non-zero
Allowed
Enabled
[1]
Disabled
WUT[5:0]
all zero
PRST[5:0]
Inhibited
Disabled
[2]
Enabled
[1]
non-zero
Allowed
Disabled
Enabled
[1]
PRST[5:0]
all zero
WUT[5:0]
Inhibited
Enabled
[1]
Disabled
[1]
Using previous values.
[2]
Wakeup divider preset to $3F.
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