A synchronous counter is a type of digital counter that consists of flip-flops, which are connected in a way that ensures their outputs change simultaneously based on a common clock signal. Unlike asynchronous counters, where flip-flops toggle independently without considering any clock signal, synchronous counters provide better synchronization and eliminate glitches that may occur during counting.
Let's understand the operation of a 4-bit synchronous counter as an example:
Basic Components:
4 D-type flip-flops (FF0, FF1, FF2, FF3): Each flip-flop has two inputs (D for data and CLK for clock) and one output (Q for the stored value).
A common clock signal (CLK): The flip-flops will change their outputs in sync with the rising or falling edge of this clock signal.
Initial State:
The flip-flops are initially set to a known state (all 0s or all 1s, depending on the design). For example, if we start with 0000, the output of FF0, FF1, FF2, and FF3 will be 0, 0, 0, and 0, respectively.
Counting Sequence:
When an external clock pulse is applied to the CLK input, all flip-flops will update their states simultaneously.
Each flip-flop receives the output (Q) from the previous flip-flop as its input (D). This creates a ripple effect down the chain of flip-flops, generating a binary counting sequence.
Synchronous Update:
The term "synchronous" refers to the fact that all flip-flops are updated simultaneously during the same clock edge. This ensures that there is no delay or uncertainty in the count propagation.
Rollover:
In a 4-bit synchronous counter, the counting sequence will repeat after reaching the maximum count, which is 1111 (15 in decimal). On the next clock pulse, it will reset back to the initial state (0000) and continue counting from there.
Binary to Decimal Conversion:
The outputs of the flip-flops represent the binary values of the counter. To convert the binary count to decimal, you can simply treat each output as a bit of a binary number and calculate the decimal equivalent. For example, if the counter output is 0101, the decimal count would be 5.
Example of the counting sequence in a 4-bit synchronous counter:
Clock (CLK) FF0 FF1 FF2 FF3 Decimal Count
0 (initial) 0 0 0 0 0
1 0 0 0 1 1
2 0 0 1 0 2
3 0 0 1 1 3
... ... ... ... ... ...
13 1 1 0 1 13
14 1 1 1 0 14
15 1 1 1 1 15
0 (reset) 0 0 0 0 0
... ... ... ... ... ...