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UM10375
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© NXP B.V. 2011. All rights reserved.
User manual
Rev. 3 — 14 June 2011
302 of 368
NXP Semiconductors
UM10375
Chapter 18: LPC13xx WatchDog Timer (WDT)
Watchdog reset or interrupt will occur any time the watchdog is running and has an
operating clock source. Any clock source works in Sleep mode, and if a watchdog
interrupt occurs in Sleep mode, it will wake up the device.
18.7.2 Watchdog Timer Constant register (WDTC - 0x4000 4004)
The WDTC register determines the time-out value. Every time a feed sequence occurs
the WDTC content is reloaded in to the Watchdog timer. It’s a 32-bit register with 8 LSB
set to 1 on reset. Writing values below 0xFF will cause 0x0000 00FF to be loaded to the
WDTC. Thus the minimum time-out interval is T
WDCLK
256
4.
18.7.3 Watchdog Feed register (WDFEED - 0x4000 4008)
Writing 0xAA followed by 0x55 to this register will reload the Watchdog timer with the
WDTC value. This operation will also start the Watchdog if it is enabled via the WDMOD
register. Setting the WDEN bit in the WDMOD register is not sufficient to enable the
Watchdog. A valid feed sequence must be completed after setting WDEN before the
Watchdog is capable of generating a reset. Until then, the Watchdog will ignore feed
errors. After writing 0xAA to WDFEED, access to any Watchdog register other than writing
0x55 to WDFEED causes an immediate reset/interrupt when the Watchdog is enabled.
The reset will be generated during the second PCLK following an incorrect access to a
Watchdog register during a feed sequence.
Interrupts should be disabled during the feed sequence. An abort condition will occur if an
interrupt happens during the feed sequence.
Table 291. Watchdog operating modes selection
WDEN
WDRESET
Mode of Operation
0
X (0 or 1)
Debug/Operate without the Watchdog running.
1
0
Watchdog interrupt mode: debug with the Watchdog interrupt but no
WDRESET enabled.
When this mode is selected, a watchdog counter underflow will set the
WDINT flag and the Watchdog interrupt request will be generated.
1
1
Watchdog reset mode: operate with the Watchdog interrupt and
WDRESET enabled.
When this mode is selected, a watchdog counter underflow will reset
the microcontroller. Although the Watchdog interrupt is also enabled in
this case (WDEN = 1) it will not be recognized since the watchdog
reset will clear the WDINT flag.
Table 292. Watchdog Constant register (WDTC - address 0x4000 4004) bit description
Bit
Symbol
Description
Reset Value
23:0
COUNT
Watchdog time-out interval.
0x0000 00FF
31:24
-
Reserved
-
Table 293. Watchdog Feed register (WDFEED - address 0x4000 4008) bit description
Bit
Symbol
Description
Reset Value
7:0
FEED
Feed value should be 0xAA followed by 0x55.
-
31:8
-
reserved
-