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MICROCONTROLLERS MADE EASY

2 ADDITIONAL MICROCONTROLLER FEATURES

2.1 TIMERS

Watchdog timer. A watchdog timer provides a means of graceful recovery from a system

problem. This could be a program that goes into an endless loop, or a hardware problem that

prevents the program from operating correctly. If the program fails to reset the watchdog at

some predetermined interval, a hardware reset will be initiated. The bug may still exist, but at

least the system has a way to recover. This is especially useful for unattended systems.

Auto Reload Timer. Compared to a standard timer, this timer automatically reloads its

counting value when the count is over, therefore sparing a waste of CPU resource.

Figure 9. Standard Timer and Auto-Reload Timer Principle

Pulse Width Modulator. Often used as a digital-to-analog conversion technique. A pulse

train is generated and regulated with a low-pass filter to generate a voltage proportional to the

duty cycle.

Figure 10. PWM Principle

Pulse Accumulator. A pulse accumulator is an event counter. Each pulse increments the

pulse accumulator register, recording the number of times this event has occurred.

Input Capture. Input Capture can measure external frequencies or time intervals by copying

the value from a free running timer into the input capture register when an external event oc-

curs.

VR02101H

TIMER

Load Register

CLOCK

CPU

Reload

End of

TIMER

Load Register

CLOCK

CPU

Reload

End of

Count

Count

STANDARD TIMER

AUTO RELOAD TIMER

VR02101I

RC Filter

CLOCK

V

time

ANALOG

VOLTAGE

PWM