UM10147_2
© NXP B.V. 2008. All rights reserved.
User manual
Rev. 02 — 28 April 2008
103 of 134
NXP Semiconductors
UM10147
P89LPC952/954 User manual
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 44. Watchdog Timer in Watchdog Mode (WDTE = 1).
PRE2
PRE1
PRE0
-
-
WDRUN
WDTOF
WDCLK
WDCON (A7H)
SHADOW REGISTER
PRESCALER
002aaa905
8-BIT DOWN
COUNTER
WDL (C1H)
watchdog
oscillator
PCLK
÷
32
MOV WFEED1, #0A5H
MOV WFEED2, #05AH
reset
(1)
Fig 45. Watchdog Timer in Timer Mode (WDTE = 0).
PRE2
PRE1
PRE0
-
-
WDRUN
WDTOF
WDCLK
WDCON (A7H)
SHADOW REGISTER
PRESCALER
002aaa939
8-BIT DOWN
COUNTER
WDL (C1H)
watchdog
oscillator
PCLK
÷
32
MOV WFEED1, #0A5H
MOV WFEED2, #05AH
interrupt