P89LPC904FD datasheet(29/41 Pages) PHILIPS

29 / 41 page

Philips Semiconductors

P89LPC904

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

Preliminary data

Rev. 02 — 25 June 2004

29 of 41

9397 750 13521

8.22 Comparator interrupt

Each 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.

8.23 Comparator and power reduction modes

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

but the comparators are 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 and Idle modes, 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.

8.24 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.

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