P87LPC762FN datasheet(21/57 Pages) PHILIPS

21 / 57 page

Philips Semiconductors

Preliminary data

87LPC762

Low power, low price, low pin count (20 pin)

microcontroller with 2 kbyte OTP

2001 Oct 26

I/O Ports

The 87LPC762 has 3 I/O ports, port 0, port 1, and port 2. The exact

number of I/O pins available depend upon the oscillator and reset

options chosen. At least 15 pins of the 87LPC762 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 87LPC762 may be software

configured to one of four types on a bit-by-bit basis, as shown in

Table 4. 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.

Table 4. Port Output Configuration Settings

PxM1.y

PxM2.y

Port Output Mode

Quasi-bidirectional

Push-Pull

Input Only (High Impedance)

Open Drain

Quasi-Bidirectional Output

Configuration

The default port output configuration for standard 87LPC762 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 pulled low, it is driven strongly and able to sink a fairly large

current. These features are somewhat similar to an open drain

output except that there are three pull-up transistors in the

quasi-bidirectional output that serve different purposes.

One of these pull-ups, called the “very weak” pull-up, is turned on

whenever the port latch for the pin contains a logic 1. The very weak

pull-up sources a very small current that will pull the pin high if it is

left floating.

A second pull-up, called the “weak” pull-up, is turned on when the

port latch for the pin contains a logic 1 and the pin itself is also at a

logic 1 level. This pull-up provides the primary source current for a

quasi-bidirectional pin that is outputting a 1. If a pin that has a logic 1

on it is pulled low by an external device, the weak pull-up turns off,

and only the very weak pull-up remains on. In order to pull the pin

low under these conditions, the external device has to sink enough

current to overpower the weak pull-up and take the voltage on the

port pin below its input threshold.

The third pull-up is referred to as the “strong” pull-up. This pull-up is

used to speed up low-to-high transitions on a quasi-bidirectional port

pin when the port latch changes from a logic 0 to a logic 1. When this

occurs, the strong pull-up turns on for a brief time, two CPU clocks, in

order to pull the port pin high quickly. Then it turns off again.

The quasi-bidirectional port configuration is shown in Figure 10.

SU01159

WEAK

VERY

WEAK

STRONG

PORT

VDD

2 CPU

CLOCK DELAY

INPUT

DATA

PORT LATCH

DATA

Figure 10. Quasi-Bidirectional Output

P87LPC762FN Datenblatt(PDF) 21 Page - NXP Semiconductors

P87LPC762FN Datenblatt(HTML) 21 Page - NXP Semiconductors

Html Pages

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57

Datenblatt Download

Link URL