P89LPC913FDH datasheet(47/66 Pages) NXP

47 / 66 page

P89LPC912_913_914_5

Product data sheet

Rev. 05 — 28 September 2007

47 of 66

NXP Semiconductors

P89LPC912/913/914

8-bit microcontrollers with two-clock 80C51 core

In order to use the Keypad Interrupt as an original KBI function like in 87LPC76x series,

the user needs to set KBPATN = 0FFH and PATN_SEL = 1 (not equal), then any key

connected to Port 0 which is enabled by the KBMASK register will cause the hardware to

set KBIF and generate an interrupt if it has been enabled. The interrupt may be used to

wake up the CPU from Idle or Power-down modes. This feature is particularly useful in

handheld, battery-powered systems that need to carefully manage power consumption

yet also need to be convenient to use.

In order to set the ﬂag and cause an interrupt, the pattern on Port 0 must be held longer

than 6 CCLKs.

8.25 Watchdog timer

The watchdog timer causes a system reset when it underﬂows as a result of a failure to

feed the timer prior to the timer reaching its terminal count. It consists of a programmable

12-bit prescaler, and an 8-bit down counter. The down counter is decremented by a tap

taken from the prescaler. The clock source for the prescaler is either the PCLK or the

nominal 400 kHz watchdog oscillator. The watchdog timer can only be reset by a

power-on reset. When the watchdog feature is disabled, it can be used as an interval timer

and may generate an interrupt. Figure 23 shows the watchdog timer in Watchdog mode.

Feeding the watchdog requires a two-byte sequence. If PCLK is selected as the watchdog

clock and the CPU is powered-down, the watchdog is disabled. The watchdog timer has a

time-out period that ranges from a few

µs to a few seconds. Please refer to the

P89LPC912/913/914

User manual for more details.

(1) Watchdog reset can also be caused by an invalid feed sequence, or by writing to WDCON not immediately followed by a

feed sequence.

Fig 23. 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)

P89LPC913FDH Datasheet(PDF) 47 Page - NXP Semiconductors

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