P89LPC952FBD datasheet(40/66 Pages) PHILIPS

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Preliminary data sheet

Rev. 01— 16 September 2005

40 of 66

Philips Semiconductors

P89LPC952

8-bit microcontroller with 10-bit ADC

7.23 KBI

The Keypad Interrupt function is intended primarily to allow a single interrupt to be

generated when Port 0 is equal to or not equal to a certain pattern. This function can be

used for bus address recognition or keypad recognition. The user can conﬁgure the port

via SFRs for different tasks.

The Keypad Interrupt Mask Register (KBMASK) is used to deﬁne which input pins

connected to Port 0 can trigger the interrupt. The Keypad Pattern Register (KBPATN) is

used to deﬁne a pattern that is compared to the value of Port 0. The Keypad Interrupt Flag

(KBIF) in the Keypad Interrupt Control Register (KBCON) is set when the condition is

matched while the Keypad Interrupt function is active. An interrupt will be generated if

enabled. The PATN_SEL bit in the Keypad Interrupt Control Register (KBCON) is used to

deﬁne equal or not-equal for the comparison.

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 six CCLKs.

7.24 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 15 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

P89LPC952 User’s Manual for more details.

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