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UM10601
All information provided in this document is subject to legal disclaimers.
© NXP B.V. 2012. All rights reserved.
Preliminary user manual
Rev. 1.0 — 7 November 2012
153 of 313
NXP Semiconductors
UM10601
Chapter 12: LPC800 Windowed Watchdog Timer (WWDT)
12.6.4 Watchdog Timer Value register
The WDTV register is used to read the current value of Watchdog timer counter.
When reading the value of the 24-bit counter, the lock and synchronization procedure
takes up to 6 WDCLK cycles plus 6 PCLK cycles, so the value of WDTV is older than the
actual value of the timer when it's being read by the CPU.
12.6.5 Watchdog Timer Warning Interrupt register
The WDWARNINT register determines the watchdog timer counter value that will
generate a watchdog interrupt. When the watchdog timer counter matches the value
defined by WARNINT, an interrupt will be generated after the subsequent WDCLK.
A match of the watchdog timer counter to WARNINT occurs when the bottom 10 bits of
the counter have the same value as the 10 bits of WARNINT, and the remaining upper bits
of the counter are all 0. This gives a maximum time of 1,023 watchdog timer counts (4,096
watchdog clocks) for the interrupt to occur prior to a watchdog event. If WARNINT is 0, the
interrupt will occur at the same time as the watchdog event.
12.6.6 Watchdog Timer Window register
The WINDOW register determines the highest WDTV value allowed when a watchdog
feed is performed. If a feed sequence occurs when WDTV is greater than the value in
WINDOW, a watchdog event will occur.
WINDOW resets to the maximum possible WDTV value, so windowing is not in effect.
Table 145. Watchdog Feed register (FEED - 0x4000 4008) bit description
Bit
Symbol
Description
Reset
Value
7:0
FEED
Feed value should be 0xAA followed by 0x55.
NA
31:8
-
Reserved, user software should not write ones to reserved
bits. The value read from a reserved bit is not defined.
NA
Table 146. Watchdog Timer Value register (TV - 0x4000 400C) bit description
Bit
Symbol Description
Reset
Value
23:0
COUNT Counter timer value.
0x00 00FF
31:24 -
Reserved, user software should not write ones to reserved bits. The
value read from a reserved bit is not defined.
NA
Table 147. Watchdog Timer Warning Interrupt register (WARNINT - 0x4000 4014) bit
description
Bit
Symbol
Description
Reset
Value
9:0
WARNINT Watchdog warning interrupt compare value.
0
31:10 -
Reserved, user software should not write ones to reserved bits. The
value read from a reserved bit is not defined.
NA