NXP Semiconductors
FXTH87E
FXTH87E, Family of Tire Pressure Monitor Sensors
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
R
7
WUF
0
6
0
5
4
3
2
1
0
WUT[5:0]
W
WUFAK
—
Reset
1
1
1
1
1
1
Table 100.ꢀPWUSC0 register field descriptions
Field
Description
Wakeup Interrupt Flag — The WUF bit indicates when a wakeup interrupt has been generated by the PWU.
This bit is cleared
7
by writing a one to the WUFAK bit. Writing a zero to this bit has no effect. Reset clears this bit.
0ꢀWakeup interrupt not generated or was previously acknowledged.
1ꢀWakeup interrupt generated.
WUF
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.
6
WUFAK
0ꢀNo effect.
1ꢀClear WUF bit.
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.
5:0
WUT[5:0]
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
Resulting
Wakeup
Interrupt
State of Control Control Bits to Resulting
Resulting
Periodic Reset
Control Bits
Bits
be Cleared
Action
non-zero
all zero
Allowed
Inhibited
Allowed
Inhibited
Enabled [1]
Disabled [2]
Disabled
Disabled
Enabled[1]
Enabled[1]
Disabled
WUT[5:0]
PRST[5:0]
PRST[5:0]
non-zero
all zero
WUT[5:0]
Enabled[1]
[1] Using previous values.
[2] Wakeup divider preset to $3F.
FXTH87ERM
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