2.1 Seven Segment Display
Seven segment display also known as seven segment indicator ,is
an electronic device that display
decimal numbers. It is used in many things; for example digital watches , electronic meters ,and basic calculators.
The seven segment consists of seven LEDs( light emitting diode) arranged
in rectangular fashion. Each of the seven LEDs is called segment because when illuminated
the segment forms parts of numerical digit to be displayed. An additional 8th
LED is sometimes used within the same package thus allowing the indication of a
decimal point ,when two or more seven segment display are connected together to
display numbers greater than ten.
The display common pin is
generally used to identify which type of seven segment display it is .As each LED
has two connecting pins, one called the Anode and the other called Cathode .the
difference between the Common Anode and the Common Cathode is the way of
connecting of the seven segments .
specially designed synchronous sequential circuits. They are usually
constructed of a number of flip flops connected in cascade, and they are very widely
used for measuring frequency and time. Counters are also similar to shift registers and other combinational circuits.
Counters are also known as digital circuit or timers. They are examples
for flip flop applications ;and here is an example of how counter works ;4-bit counter is consists of 4 stages of cascaded J-K flip-flops. This
is a binary counter, since the output is in binary system format, i.e., only
two digits are used to represent the count, i.e., ‘1’ and ‘0’. With only
4 bits, it can only count up to ‘1111’, or decimal number 15.
The output of counters is based on the clock
pulse application it can be used to count the number of pulses. We have two types of counters; the first one is when the counter has
only one clock ip given to all flip flops
it is a synchronous counter, otherwise if the counter op the flip flops is the
clock signal nearby one it is asynchronous counter.
(You should write few (two to three)
paragraphs about the counters).
2.3 Types of Counters
2.3.1 Asynchronous counter
In a 2 bit asynchronous counter, the exterior clock is connected
to the clock of the first flip flop and it changes the state at a decreasing
edge of every clock pulse, however in the second flip flop it changes only when
it is activated by the decreasing edge of Q of the first flip flop. The circuit
diagram of the two-bit ripple counter includes four different states each one
is consisting with a count value. Likewise, a counter with n flip flops can have
2n states. The number of state in a counter is called as its mod number. Therefore,
a two-bit counter is a mod-4 counter.
2.3.2 synchronous counter
In the synchronous counter , the CLK i/ps of all the FFs are connected
together and are activated by the i/p pulses. So, all the FFs change states
instantaneously. The circuit diagram below is a three bit synchronous counter.
The inputs J and K of flip-flop0 are connected to HIGH. Flip-flop 1 has its J
&K i/ps connected to the o/p of flip-flop0 (FF0), and the inputs J & K
of flip-flop2 (FF2) are connected to the o/p of an AND gate that is fed by the
o/ps of flip-flop0 and flip-flop1. When the both the outputs of FF0 & FF1
are HIGH. The positive edge of the fourth CLK pulse will cause FF2 to alter its
state because of the AND gate.
In the end this is
some proptes for each one
a. Are also known as ripple counters;
b. are very simple;
c. use the minimum possible hardware (logic gates); employ flip-flops connected
serially, with each one triggering (clocking) the next;
d. have an overall
count which ‘ripples’ through, meaning the overall operation
is relatively slow;
e. require virtually no design.
a. use interconnected flip-flops, but all are clocked together by the system
b. use the outputs from the flip-flops, to determine the next states of the
following flip-flops (rather than simply clocking them);
c. require no settling time due to rippling (as all flip-flops are clocked
d. need designing, to determine how the present state of the circuit must be
used to determine the next state (i.e. count);
1.4 Application of Counters
digital counter is a device that generates binary numbers in a specified count
sequence. The counter progresses through the specified sequence of numbers when
triggered by an incoming clock waveform, and it advances from one number to the
next only on a clock pulse. The counter cycles through the same sequence of
numbers continuously so long as there is an incoming clock pulse. The binary
number sequence generated by the digital counter can be used in logic systems
to count up or down, to generate truth table input variable sequences for logic
circuits, to cycle through addresses of memories in microprocessor applications,
to generate waveforms of specific patterns and frequencies, and to activate
other logic circuits in a complex process