UM10503
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© NXP B.V. 2012. All rights reserved.
User manual
Rev. 1.3 — 6 July 2012
920 of 1269
NXP Semiconductors
UM10503
Chapter 34: LPC43xx Windowed Watchdog timer (WWDT)
34.5.2 WWDT behavior in the power-down modes
The WWDT is running in Sleep mode. A watchdog triggered reset in Sleep mode resets
and wakes up the chip. Likewise, a watchdog triggered interrupt wakes up the chip from
Sleep mode if the interrupt is enabled in the NVIC.
The WWDT is not operating in Deep-sleep, Power-down, and Deep power-down modes.
34.6 Clocking
The watchdog timer block uses two clocks: PCLK and WDCLK. PCLK is used for the APB
accesses to the watchdog registers and is derived from the BASE_M4_CLK. The WDCLK
is used for the watchdog timer counting and is derived from the IRC. The clock source (the
IRC) is fixed to ensure that the WDT always has a valid clock.
There is some synchronization logic between these two clock domains. When the MOD
and TC registers are updated by APB operations, the new value will take effect in three
WDCLK cycles on the logic in the WDCLK clock domain. When the watchdog timer is
counting the WDCLK clock cycles, the synchronization logic will first lock the value of the
counter on WDCLK and then synchronize it with the PCLK for reading when the TV
register by the CPU.
34.7 Register description
The Watchdog registers are shown in
[1]
Reset value reflects the data stored in used bits only. It does not include reserved bits content.
34.7.1 Watchdog mode register
The WDMOD register controls the operation of the Watchdog as per the combination of
WDEN and RESET bits. Note that a watchdog feed must be performed before any
changes to the WDMOD register take effect.
Table 772. Register overview: Watchdog timer (base address 0x4008 0000)
Name
Access Address
offset
Description
Reset
value
Reference
MOD
R/W
0x000
Watchdog mode register. This register contains the basic
mode and status of the Watchdog Timer.
0
TC
R/W
0x004
Watchdog timer constant register. This register determines
the time-out value.
0xFF
FEED
WO
0x008
Watchdog feed sequence register. Writing 0xAA followed by
0x55 to this register reloads the Watchdog timer with the
value contained in WDTC.
NA
TV
RO
0x00C
Watchdog timer value register. This register reads out the
current value of the Watchdog timer.
0xFF
-
-
0x010
Reserved
-
-
WARNINT
R/W
0x014
Watchdog warning interrupt register. This register contains
the Watchdog warning interrupt compare value.
0
WINDOW
R/W
0x018
Watchdog timer window register. This register contains the
Watchdog window value.
0xFF FFFF