Counter/Timers (8254)
OVERVIEW
Three programmable 16-bit counter/timers on the ZT 8809A are
implemented in an Intel 8254 chip. These timers can handle inputs
from DC to 8 MHz, and are useful for generation of accurate time
delays under software control.
This chapter describes the main components of the counter/timers, the
method used to program them, and their use by STD DOS and the
STD ROM Development System.
In general, these counter/timers are used in place of a software timing
loop or for event tracking.
When used for a timing loop, the
programmer configures a timer for the proper time delay, and some
time later an interrupt from the timer signifies that this time delay has
passed. When used for an event counter, the programmer initializes
the counter with a desired value. After the counter has counted down
to zero, an interrupt occurs indicating that the proper number of
events has passed.
Some of the other counter/timer functions include:
–
Real-time clock
–
Digital one-shot
–
Programmable rate generator
–
Square wave generator
–
Binary rate multiplier
–
Complex waveform generator
–
Complex motor controller
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