UM10503
All information provided in this document is subject to legal disclaimers.
© NXP B.V. 2012. All rights reserved.
User manual
Rev. 1.3 — 6 July 2012
923 of 1269
NXP Semiconductors
UM10503
Chapter 34: LPC43xx Windowed Watchdog timer (WWDT)
34.7.4 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.
34.7.5 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 WDWARNINT, an interrupt will be generated after the subsequent WDCLK.
A match of the watchdog timer counter to WDWARNINT 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
WDWARNINT is set to 0, the interrupt will occur at the same time as the watchdog event.
34.7.6 Watchdog timer window register
The WDWINDOW register determines the highest WDTV value allowed when a watchdog
feed is performed. If a feed valid sequence completes prior to WDTV reaching the value in
WDWINDOW, a watchdog event will occur.
WDWINDOW resets to the maximum possible WDTV value, so windowing is not in effect.
Values of WDWINDOW below 0x100 will make it impossible to ever feed the watchdog
successfully.
Table 776. Watchdog Feed register (FEED - 0x4008 0008) bit description
Bit
Symbol
Description
Reset value
7:0
Feed
Feed value should be 0xAA followed by 0x55.
NA
Table 777. Watchdog Timer Value register (TV - 0x4008 000C) 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 778. Watchdog Timer Warning Interrupt register (WARNINT - 0x4008 0014) bit
description
Bit
Symbol
Description
Reset value
9:0
WDWARNINT
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