P89LPC9103 datasheet(39/61 Pages) NXP

39 / 61 page

P89LPC9102_9103_9107_3

Product data sheet

Rev. 03 — 10 July 2007

39 of 61

NXP Semiconductors

P89LPC9102/9103/9107

8-bit microcontrollers with two-clock accelerated 80C51 core

8.21 Comparator interrupt

The comparator has an interrupt ﬂag contained in its conﬁguration register. This ﬂag is set

whenever the comparator output changes state. The ﬂag may be polled by software or

may be used to generate an interrupt.

8.22 Comparator and power reduction modes

The comparator may remain enabled when Power-down mode or Idle mode is activated,

but the comparator is disabled automatically in Total Power-down mode.

If the comparator interrupt is enabled (except in Total Power-down mode), a change of the

comparator output state will generate an interrupt and wake-up the processor. If the

comparator output to a pin is enabled, the pin should be conﬁgured in the push-pull mode

in order to obtain fast switching times while in Power-down mode. The reason is that with

the oscillator stopped, the temporary strong pull-up that normally occurs during switching

on a quasi-bidirectional port pin does not take place.

The comparator consumes power in Power-down mode and Idle mode, as well as in the

normal operating mode. This fact should be taken into account when system power

consumption is an issue. To minimize power consumption, the user can disable the

comparator via PCONA.5 or put the device in Total Power-down mode.

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 mode or Power-down mode. 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.

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

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