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Chapter 8

Signal Generation

8.1 Objective

To become familiar with generating square waves.

8.2 Background

In an earlier lab, you had to generate a square wave signal using various interrupts.

This lab builds on this. For a general square wave signal, we deﬁne the on-time,

, the oﬀ-time, T

oﬀ

, and the period T as shown in the ﬁgure 7.1. The goal of

the lab is to generate such square waves. The ratio

is called the duty cycle

and is expressed as a percentage. When dealing with time it is convenient to talk

in terms of clock ticks. The HC11 has a 2 MHz e-clock, or you have 2 × 10

ticks

per second. Hence 1 clock tick is 0.5 microseconds.

-¾

oﬀ

T = T

+ T

oﬀ

0 Volts

5 Volts

Figure 8.1: 0-5 volt square wave

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Motorola Axiom CMD11E1 Guida Utente Pagina 87