Lista Exercicios Sistemas Embarcados

1 - O que é porta paralela?

Parallel input/output (I/O) is the workhorse for all the basic data

interchange of a microcontroller, including interfacing with switches, LEDs, displays and so

on. A group of parallel I/O interconnections, appearing on the pins of the microcontroller, is

called a ‘parallel port’.

Entrada / saída (I / O) é o carro-chefe para todos intercâmbio de dados básico de um microcontrolador, incluindo interface com interruptores, LEDs, displays e assim por diante. Um grupo de paralelo I / O interconexões, aparecendo nos pinos do microcontrolador, é chamado de "porta paralela".

2 - O que é uma entrada Schmitt trigger?

A Schmitt trigger (Figure 3.5) is a certain type of logic gate input which is designed to ‘clean

up’ a corrupted logic signal. It has two input thresholds, with the ‘positive-going’ higher than

the ‘negative-going’. A signal starting from a low value has to pass the negative-going

threshold (at which point nothing happens) and then cross the ‘positive-going’ threshold, at

which point the output changes state. The output will not reverse until the input (now negative going) has returned to the negative-going threshold. Thus, small fluctuations which recross

a threshold just crossed do not cause any change in output.

Um gatilho Schmitt (Figura 3.5) é um certo tipo de entrada de porta lógica que é projetado para 'limpar' um sinal de lógica corrompido. Ele tem dois limiares de entrada, com a "positiva contínua 'maior do que o' negativo curso". Um sinal a partir de um valor baixo tem de passar o limiar negativo curso (em que nada acontece ponto) e depois cruzar o limiar "positiva contínua ', altura em que a saída muda de estado. A saída não será revertida até que a entrada (agora vai negativo) voltou a ser o limite negativo-going. Assim, pequenas flutuações que recross um limite apenas cruzou não causam qualquer mudança na produção.

3 - Qual a corrente típica necessária para acender um LED?

For a single LED to be comfortably visible, it typically requires around 10mA of current.

Para um único LED para ser confortavelmente visível, que normalmente exige em torno de 10mA de corrente.

4 - Quais os modos possíveis de operação do oscilador de clock do PIC16F84?

The user selects which mode is to be used by setting bits in the Configuration Word (Figure 2.6).

_ XT – crystal. This is the standard crystal configuration. It is intended for crystals or

resonators in the range 1–4 MHz.

_ HS – high speed. This is a higher drive version of the XT configuration. It recognises that

higher-frequency crystals, and ceramic resonators in general, require a higher drive

current. It is intended for crystal frequencies in the region of 4 MHz or greater, and/or

ceramic resonators. It leads to the highest current consumption of all the oscillator modes.

_ LP – low power. This mode is intended for low-frequency crystal applications and gives

the lowest power consumption possible. In many cases this will be 32.768 kHz (i.e. 215),

which is the most popular frequency for low-power, time-sensitive applications, for

example wristwatches. It will, however, operate at any frequency below around 200 kHz.

_ RC – resistor–capacitor. For this an external resistor and capacitor must be connected

to pin 16, replicating the circuit of Figure 3.13(a). This is the lowest-cost way of getting

an oscillator, but should not be used when any timing accuracy is required. The nominal

frequency of oscillation can be predicted with limited accuracy only, and even then it

will drift with changing temperature, supply voltage and time. An example of a use of

the RC oscillator appears in the electronic ping-pong game case study at the end of this

chapter.

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