Introduction to counter
A Counter is a register that goes through a predetermined sequence of states upon the application of clock pulses. A group of flip-flops connected together forms a registers.
A register is used solely for storing and shifting data which is in the form of ls and 0s, from an external source. A counter is a register capable of counting the number of clock pulses arriving at its clock input.
Count represents the number of clock pulses arrived. A specified sequence of states appears as the counter output.
This is the main difference between the register and counter. A specified sequence of states is different for different types of counters.
There are two types of counters, synchronous and asynchronous. In synchronous counter, the common clock input is connected to all of the flip-flops and thus they are clocked simultaneously. In asynchronous counter, commonly called, ripple counters, the first flip-flop is clocked by the external clock pulse and then each successive flip-flop is clocked by Q or Q output of previous flip flop.
Therefore, in an asynchronous counter the flip-flop are not clocked simultaneously. The Figure 8.1 shows the logic symbol ofa binary counter. External clock is applied to the clock input of the counter. The counter can be positive edge triggered or negative edge triggered. The n-bit binary counter has n flip-flop, and it has 2 distinct states of outputs. For example :2 bit counter has 2 flip-flop and it has 4(2 2 ) distinct states: 00,01,10,11
Types of Counter
There are two types of counters available for digital circuits, they are:
- Ripple/Asynchronous Counter
- Synchronous Counter
The following table shows the difference between the Asynchronous and Synchronous counter:
Difference between Synchronous and Asynchronous Counter
- Flip flop are connected in such a way that the output of first flip flop drives the clock of next flip flop.
- Flip flop are not clocked simultaneously
- Logic Circuit is very simple even for more number of states
- Speed is slow as clock is propagated through number of stages
- Less number of logic gates required.
- These are slow in operation
- Low Cost
- For asynchronous counters, Standard logic synchronous packages are not available .
- There is no connection between output of the first flip flop and clock of next flip-flop.
- All Flip flop are clocked simultaneously
- Circuit becomes complicated as number of states increases.
- Speed is high as clock is given at a same time.
- Large numbers of logic gates are required to design.
- These are faster than that of Ripple counter
- High Cost
- Standard logic packages available for synchronous.
Digital Computer ?
A digital computer is an electronics device that read the data from the environment through the input device,