Computers as Components, 2nd Edition

4.3 I/O Devices 171

Reset

CPU

Time-out

Watchdog

timer

FIGURE 4.18

A watchdog timer.

the watchdog timer,before the timer ever reaches its time-out limit. If the watchdog

timer ever does reach that limit, its time-out action is to reset the processor. In that

case,the presumption is that either a software flaw or hardware problem has caused

the CPU to misbehave. Rather than diagnose the problem,the system is reset to get

it operational as quickly as possible.

4.3.2 A/D and D/A Converters

Analog/digital (A/D) and digital/analog (D/A) converters (typically known

as ADCs and DACs, respectively) are often used to interface nondigital devices to

embedded systems.