P89LPC907FD datasheet(38/51 Pages) PHILIPS

38 / 51 page

Philips Semiconductors

P89LPC906/907/908

8-bit microcontrollers with two-clock 80C51 core

Product data

Rev. 05 — 17 December 2004

38 of 51

9397 750 14467

8.21 Comparator and power reduction modes

The comparator may remain enabled when Power-down 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 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.

8.22 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

Fig 16. Comparator input and output connections.

Comparator

(P0.4) CIN1A

(P0.5) CMPREF

VREF

OE1

CO1

002aaa468

CMP1 (P0.6)

Change Detect

CMF1

Interrupt

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