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NXP Semiconductors
QN902x
User Manual of QN902x
UM10996
All information provided in this document is subject to legal disclaimers.
© NXP Semiconductors N.V. 2018. All rights reserved.
User Manual
Rev 1.3
— 05 November 2018
103 of 128
13.
Watch-Dog Timer (WDT)
The Watchdog timer (WDT) is a 32-bit down-count timer intended as a recovery method
in situations where the CPU may be subjected to software upset.
13.1
Functional Description
The WDT resets the system when the software fails to clear the WDT within the selected
time interval. The WDT can be configured either as a Watchdog Timer or as a timer for
general-purpose use. If the watchdog function is not needed in an application, it is
possible to configure the Watchdog Timer to be used as an interval timer that can be used
to generate interrupts at selected time intervals. The maximum timeout interval is 1.5
days. The WDT is initialized from the Reload Register, WDOGLOAD. The module generates
a regular interrupt, WDOGINT, depending on a programmed value. The counter
decrements by one on each positive clock edge of WDOGCLK when the clock enable,
WDOGCLKEN, is HIGH. The watchdog monitors the interrupt and asserts a reset
WDOGRES signal, when the counter reaches 0, and the counter is stopped. On the next
enabled WDOGCLK clock edge, the counter is reloaded from the WDOGLOAD register and
the count-down sequence continues. If the interrupt is not cleared by the time that the
counter next reaches 0, then the watchdog module reasserts the reset signal.
Watchdog is
programmed
Counter reaches
zero
Counter reaches
zero
Counter reloaded
and count down
without reprogram
Count down
without reprogram
If INTEN bit in WDOGCONTROL register
is set to 1, WDOGINIT is asserted
If RESEN bit in WDOGCONTROL register
is set to 1, WDOGRES is asserted
Figure 12 Watchdog Operation Flow Diagram
13.2
Register Description
13.2.1
Register Map
The RTC registers’ base address is 0x4000_1000.
Table 76 Timer Register Map
Offset
Name
Description
000h
LOAD
Contains the value from which the counter is to
decrement. When this register is written to, the count is
immediately restarted from the new value. The
minimum valid value is 1.
004h
VALUE
Current value of the decrementing counter.
008h
CTRL
R/W register that enables the software to control the