AN887 Datasheet, PDF (6/12 Pages) STMicroelectronics – MICROCONTROLLERS MADE EASY

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
CLOCK
STANDARD TIMER
TIMER
End of
Count
Load Register
Reload
CPU
AUTO RELOAD TIMER
CLOCK
TIMER
End of
Count
Load Register
Reload
CPU
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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
CLOCK
ANALOG
V
VOLTAGE
PWM
RC Filter
time
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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.
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