P87LPC779 datasheet(29/74 Pages) PHILIPS

29 / 74 page

Philips Semiconductors

P87LPC779

CMOS single-chip 8-bit microcontroller

Product data

Rev. 02 — 03 May 2004

29 of 74

9397 750 13213

8.9 I/O ports

The P87LPC779 has 3 I/O ports, port 0, port 1, and port 2. The exact number of I/O

pins available depends upon the oscillator and reset options chosen. At least 15 pins

of the P87LPC779 may be used as I/Os when a two-pin external oscillator and an

external reset circuit are used. Up to 18 pins may be available if fully on-chip oscillator

and reset conﬁgurations are chosen.

All but three I/O port pins on the P87LPC779 may be software conﬁgured to one of

four types on a bit-by-bit basis, as shown in Table 20. These are: quasi-bidirectional

(standard 80C51 port outputs), push-pull, open drain, and input only. Two

conﬁguration registers for each port choose the output type for each port pin.

8.9.1

Quasi-bidirectional output conﬁguration

The default port output conﬁguration for standard P87LPC779 I/O ports is the

quasi-bidirectional output that is common on the 80C51 and most of its derivatives.

This output type can be used as both an input and output without the need to

reconﬁgure the port. This is possible because when the port outputs a logic HIGH, it

is weakly driven, allowing an external device to pull the pin LOW. When the pin is

Fig 9.

Interrupt sources, interrupt enables, and Power-down wake-up sources.

002aaa627

IE0

EX0

IE1

EX1

BOD

EBO

KBF

EKB

INTERRUPT

TO CPU

WAKE-UP

(IF IN POWER-

DOWN)

EC2

CM2

EWD

WDT

EAD

ADC

EC1

CM1

EA (from IE0 register)

TF0

ET0

TF1

ET1

RI & TI

ATN

EI2

TIMER 1 INTERRUPT

ETI

Table 20:

Port output conﬁguration settings

PxM1.y

PxM2.y

Port output mode

Quasi-bidirectional

Push-Pull

Input Only (High Impedance)

Open Drain

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