Author :
Craig
Steiner
Source :
8052.com
Book :
The
8051/8052
Microcontroller:
Architecture,
Assembly
Language,
And
Hardware
Interfacing
(Paperback)
USING
TIMERS
AS EVENT
COUNTERS
We've
discussed
how a
timer
can be
used for
the
obvious
purpose
of
keeping
track of
time.
However,
the 8051
also
allows
us to
use the
timers
to count
events.
How can
this be
useful?
Let's
say you
had a
sensor
placed
across a
road
that
would
send a
pulse
every
time a
car
passed
over it.
This
could be
used to
determine
the
volume
of
traffic
on the
road. We
could
attach
this
sensor
to one
of the
8051's
I/O
lines
and
constantly
monitor
it,
detecting
when it
pulsed
high and
then
incrementing
our
counter
when it
went
back to
a low
state.
This is
not
terribly
difficult,
but
requires
some
code.
Let's
say we
hooked
the
sensor
to P1.0;
the code
to count
cars
passing
would
look
something
like
this:
|
JNB P1.0,$ |
;If a car hasn't raised the signal, keep waiting |
|
JB P1.0,$ |
;The line is high which means the car is on the sensor right now |
|
INC COUNTER |
;The car has passed completely, so we count it |
>>>
Enter
here for
detail
on
Timers
as Event
Counters
<<<
<<< Click
here to
come
back on
(8051
-
Timers)
