UM10462
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User manual
Rev. 5.5 — 21 December 2016
376 of 523
NXP Semiconductors
UM10462
Chapter 17: LPC11U3x/2x/1x Windowed Watchdog Timer (WWDT)
17.8.4 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.
17.8.5 Watchdog Clock Select register
The LOCK bit in this register prevents software from changing the clock source
inadvertently. Once the LOCK bit is set, software cannot change the clock source until this
register has been reset from any reset source.
17.8.6 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 WARNINT
is 0, the interrupt will occur at the same time as the watchdog event.
Table 340. 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 341. 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 342. Watchdog Clock Select register (CLKSEL - 0x4000 4010) bit description
Bit
Symbol
Value
Description
Reset
Value
0
CLKSEL
Selects source of WDT clock
0
0
IRC
1
Watchdog oscillator (WDOSC)
30:1 -
Reserved, user software should not write ones to reserved
bits. The value read from a reserved bit is not defined.
NA
31
LOCK
If this bit is set to one, writing to this register does not affect bit
0 (that is the clock source cannot be changed). The clock
source can only by changed after a reset from any source.
0