Counter

The counter is a sequential circuit that uses a register to generate a sequence of numbers. The simplest numerator generates a sequence of ascending consecutive numbers. The size of the counter is given by the number of bits of the registers used.

The schematic of this device is as follows:

Note: The count can be used as a frequency divider because each bit has a period twice as high as the previous one, and the bit 0 has a double period over the clock signal:

Value	0	1	2	3	4	5	6	7	8	9	10	11	12	13	14	15	Waveforms
Bit 0	0	1	0	1	0	1	0	1	0	1	0	1	0	1	0	1
Bit 1	0	0	1	1	0	0	1	1	0	0	1	1	0	0	1	1
Bit 2	0	0	0	0	1	1	1	1	0	0	0	0	1	1	1	1
Bit 3	0	0	0	0	0	0	0	0	1	1	1	1	1	1	1	1

Interface of a counter

The interface of a numerator necessarily contains the following ports:

• Clock signal port;
• output signal port, which is even the counting register.

In addition, there may still be:

• Reset port;
• port that controls the counting direction;
• port that stops or starts counting;
• port giving the maximum value the numerator can reach;
• port that commands to load a start value in the counter of the counter and the port on which this value is given;
• etc.

Implementing a counter

As a sequential circuit, a counter is implemented exclusively with always sequential blocks.