Counters are found in many places where you might not expect to find them.
Here are a few places where you would see counters.
In a DMM (Digital MultiMeter)
a voltage is measured and displayed digitally. Inside the DMM, the
A/D
(Analog-to-Digital) converter probably uses a counter
in the process of converting the analog voltage signal to a digital equivalent.
A real estate agent uses
a gadget she places on a wall to measure interior dimensions (distance
between walls). The gadget uses a counter
to time how long it takes an acoustical signal to travel across the room
and return after reflecting off the opposite wall.
You drive across two rubber
tubes stretched across the pavement. A counter
starts running when you hit the first one, and stops when you hit the second
one. That way the police know how fast you were going and tell you
that when the ticket comes in the mail.
You can see that there are many places where
counters are built into equipment. They are found in many different
kinds of equipment and they are devices that you really need to know about.
The
Toggle (T) Flip-flop - A One Stage Counter
A toggle flip-flop is really a single bit counter. You should have
encountered the T flip-flop in the lesson on flip-flops.
Here is a simulation of a T flip-flop from that lesson.
Simulation
In this simulation, there are two (2) T flip-flops. One T flip-flop
is driven by the clock, but the second T flip-flop is driven by the output
of the first one.
The Pulse button generates
a short pulse - depending, of course, on how fast you can click the mouse
on the clock button.
Note that the input pulse
to the flip-flop is ON for a short while, then goes OFF.
When the input pulse goes
OFF, the output of the first flip-flop changes.
When the output of the
first flip-flop goes OFF, the second flip-flop changes state.
The
simulation shows how two T flip-flops can work as a counter to count clock
pulses. The question buried in this is whether that will continue
to work for larger structures with T flip-flops. Here's a simulation
where you can check that.
Simulation
In this simulation, there are four (4) T flip-flops. One T flip-flop
is driven by the clock, but the inputs to all of the other T flip-flops
are just outputs from the preceding T flip-flop. Check the circuit
by clicking the clock button (a lot of times!).
OR,
Use this version in which the clock runs continuously (one complete pulse
each second).
Questions
Q1
In the four bit counter above, does it count UP
or DOWN?
Q2
In the four bit counter above, look at the inverted outputs (coming out
of the inverters above the flip-flops). Do they seem to count UP
or DOWN?
Now, there's something interesting in all this. Not only have we
built a counter, but we have a counter that can be thought of as counting
up or counting down. Consider the following.
