UM10346_1
© NXP B.V. 2009. All rights reserved.
User manual
Rev. 01 — 2 November 2009
102 of 132
NXP Semiconductors
UM10346
LPC980/982 User manual
Otherwise, the watchdog could become disabled when CCLK turns off. The watchdog
oscillator will never become selected as the clock source unless CCLK is turned on again
first.
15.4 Watchdog Timer in Timer mode
shows the Watchdog Timer in Timer Mode. In this mode, any changes to
WDCON are written to the shadow register after one watchdog clock cycle. A watchdog
underflow will set the WDTOF bit. If IEN0.6 is set, the watchdog underflow is enabled to
cause an interrupt. WDTOF is cleared by writing a logic 0 to this bit in software. When an
underflow occurs, the contents of WDL is reloaded into the down counter and the
watchdog timer immediately begins to count down again.
A feed is necessary to cause WDL to be loaded into the down counter before an
underflow occurs. Incorrect feeds are ignored in this mode.
Fig 47. Watchdog Timer in Watchdog Mode (WDTE = 1)
PRE2
PRE1
PRE0
-
-
WDRUN
WDTOF
WDCLK
WDCON (A7H)
SHADOW REGISTER
PRESCALER
002aae542
8-BIT DOWN
COUNTER
WDL (C1H)
watchdog
oscillator
400 kHz
oscillator
25 kHz
oscillator
crystal
oscillator
PCLK
XTALWD
(CLKCON.4)
WDMOD
(CLKCON.5)
÷
32
0
1
0
1
MOV WFEED1, #0A5H
MOV WFEED2, #05AH
reset
0
1