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UM10316_0
© NXP B.V. 2008. All rights reserved.
User manual
Rev. 00.06 — 17 December 2008
297 of 571
NXP Semiconductors
UM10316
Chapter 20: LPC29xx WatchDog Timer (WDT)
To generate Watchdog interrupts in Watchdog debug mode the interrupt has to be
enabled via the interrupt enable register. A Watchdog overflow interrupt can be cleared by
writing to the clear-interrupt register.
Another way to prevent resets during debug mode is via the pause feature of the
Watchdog timer. The Watchdog is stalled when the ARM9 is in debug mode and the
PAUSE_ENABLE bit in the Watchdog Timer Control register is set.
A Watchdog reset is equal to an external reset: the program counter will start from
0x0000 0000 and registers are cleared. The Reset Generation Unit contains a reset
source register to determine the reset source when the device has gone through a reset.
See
4.
Watchdog register overview
The Watchdog timer registers are shown in
.
The timer registers have an offset to the base address WDT RegBase. This can be found
in the memory map, see
4
Write 0x251D8951 (key exor
counter_enable) to the Watchdog Timer
Control register. The timer is now started
Write time-out value (e.g.0x0000FFFF)
to the Watchdog time-out register.
This indicates time-out reset at 65,536
clock cycles. It is now locked again.
5
Write 0x251D8950 (key) to the
Watchdog key register (0x038) at
periodical intervals to restart
Timer_Counter.
Write before time-out occurs !
Write 0x251D8951 (key exor
counter_enable) to the Watchdog timer
control register. The timer is now started
6
-
Write 0x251D8950 (key) to the
Watchdog key register (0x038) at
periodical intervals to restart
Timer_Counter.
Write before time-out occurs !
Table 250. Watchdog programming steps
Step
Normal mode
Debug mode
Table 251. Watchdog timer register overview (base address 0xE004 0000)
Address
offset
Access
Reset value
Name
Description
Reference
000h
R/W
0h
WTCR
Timer control register
see
004h
R/W
0000 0000h
TC
Timer counter value
see
008h
R/W
0000 0000h
PR
Prescale register
see
038h
R/W
251D 8950h
WD_KEY
Watchdog key register
see
03Ch
R/W
FFFF FFFFh
WD_TIMEOUT
Watchdog time-out register
see
040h
R/W
0000 0000h
WD_DEBUG
Watchdog debug register
see