Embedded Systems Design with the Atmel AVR Microcontroller Part II

CHAPTER 6
Timing Subsystem
Objectives: After reading this chapter, the reader should be able to
Explain key timing system related terminology.
Compute the frequency and the period of a periodic signal using a microcontroller.
Describe functional components of a microcontroller timer system.
Describe the procedure to capture incoming signal events.
Describe the procedure to generate time critical output
signals.
Describe the timing related features of the Atmel ATmega164.
Describe the four operating modes of the Atmel ATmega164 timing system.
Describe the register configurations for the ATmega164’s Timer 0, Timer 1, and Timer 2.
Program the ATmega164 timer system for a variety of applications.
6.1 OVERVIEW
One of the most important reasons for using microcontrollers in embedded systems is the capabilities
of microcontrollers to perform time related tasks. In a simple application, one can program a
microcontroller system to turn on or turn off an external device at a programmed time. In a more
involved application, we can use a microcontroller to generate complex digital waveforms with varying
pulse widths to control the speed of a DC motor. In this chapter, we review the capabilities of
the Atmel ATmega164 microcontroller to perform time related functions. We begin with a review
of timing related terminology. We then provide an overview of the general operation of a timing
system followed by the timing system features aboard the ATmega164. Next, we present a detailed
discussion of each of its timing channels: Timer 0, Timer 1, and Timer 2 and their different modes
of operation.
6.2 TIMING RELATED TERMINOLOGY
6.2.1 FREQUENCY
Consider signal x(t) that repeats itself. We call this signal periodic with period T, if it satisfies
137