P89LPC902FD datasheet(39/55 Pages) PHILIPS

39 / 55 page

Philips Semiconductors

P89LPC901/902/903

8-bit microcontrollers with two-clock 80C51 core

Product data

Rev. 04 — 21 November 2003

39 of 55

9397 750 12293

8.23 Keypad interrupt (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 6 CCLKs.

8.24 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 20 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

afew

µs to a few seconds. Please refer to the P89LPC901/902/903 User’s Manual for

more details.

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