P87LPC779FDH datasheet(33/74 Pages) PHILIPS

33 / 74 page

Philips Semiconductors

P87LPC779

CMOS single-chip 8-bit microcontroller

Product data

Rev. 02 — 03 May 2004

33 of 74

9397 750 13213

8.9.4

Keyboard interrupt (KBI)

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

generated when any key is pressed on a keyboard or keypad connected to speciﬁc

pins of the P87LPC779, as shown in Figure 13. This 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.

The P87LPC779 allows any or all pins of port 0 to be enabled to cause this interrupt.

Port pins are enabled by the setting of bits in the KBI register, as shown in Tables 23

and 24. The Keyboard Interrupt Flag (KBF) in the AUXR1 register is set when any

enabled pin is pulled LOW while the KBI interrupt function is active. An interrupt will

be generated if it has been enabled. Note that the KBF bit must be cleared by

software.

Due to human time scales and the mechanical delay associated with keyswitch

closures, the KBI feature will typically allow the interrupt service routine to poll port 0

in order to determine which key was pressed, even if the processor has to wake up

from Power-down mode. Refer to Section 8.12 “Power reduction modes” on page 38

for details.

Fig 13. Keyboard interrupt.

Table 23:

KBI - Keyboard interrupt register (address 86H) bit allocation

Not bit addressable; Reset value: 00H

Bit

Symbol

KBI.7

KBI.6

KBI.5

KBI.4

KBI.3

KBI.2

KBI.1

KBI.0

002aaa631

P0.7

KBI.7

P0.6

KBI.6

P0.5

KBI.5

P0.4

KBI.4

P0.3

KBI.3

P0.2

KBI.2

P0.1

KBI.1

P0.0

KBI.0

KBF

(KBI interrupt)

EKB

(from IEN1

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