A synchronous counter is a type of digital circuit that counts a sequence of binary numbers in a predetermined order. It consists of flip-flops, which are memory elements capable of storing binary values (0 or 1). These flip-flops are connected in such a way that their outputs are used to represent the binary count.
Let's understand the working of a 4-bit synchronous counter as an example. A 4-bit synchronous counter can count from 0 (0000 in binary) to 15 (1111 in binary).
Flip-flops: A 4-bit synchronous counter will have four flip-flops, labeled as FF0, FF1, FF2, and FF3, each representing one bit of the count.
Clock signal: All the flip-flops in the counter are driven by the same clock signal (usually denoted as CLK). The clock signal serves as a timing reference, and the counter updates its count on every rising or falling edge of the clock, depending on its design.
Clear and preset inputs: The counter usually has a clear input (CLR) to reset the counter to a specific value, and a preset input (PRE) to load a specific value into the counter.
Connections between flip-flops: The outputs of the flip-flops are connected to form the binary count. The output of FF0 is the least significant bit (LSB), and the output of FF3 is the most significant bit (MSB).
Feedback connection: To make the counter count in a specific sequence, feedback connections are made from certain flip-flop outputs to the inputs of others. This creates a "ripple effect" when the counter increments.
Now, let's go through the counting process:
Initially, all flip-flop outputs are set to 0 (0000), representing the count value 0.
When the clock signal (CLK) rises or falls (depending on the design), the counter advances to the next count.
At each clock edge, the binary count is incremented by 1. This is achieved by the feedback connections from higher-order flip-flops to lower-order flip-flops. For example, if the counter is at 0111 (decimal 7), the next clock edge will trigger a carry from FF0 to FF1, resulting in 1000 (decimal 8).
The counting sequence continues until it reaches the maximum count, which, in this case, is 1111 (decimal 15).
At the maximum count, the next clock edge will cause the counter to wrap around and start from 0000 again, repeating the counting sequence.
The clear (CLR) input can be used to reset the counter to 0, and the preset (PRE) input can be used to load a specific value into the counter, allowing for non-sequential counting sequences if desired.
In summary, a synchronous counter uses a common clock signal to update its count on every clock edge. The feedback connections between flip-flops determine the counting sequence, and the binary count is represented by the outputs of the individual flip-flops.