A 4-bit parallel adder is a digital circuit that is used to perform arithmetic operations, specifically addition, on two 4-bit binary numbers. It is called a parallel adder because it performs the addition simultaneously on all the bits of the two input numbers.

The basic principle of a 4-bit parallel adder is the same as that of a 1-bit adder, which consists of two inputs (A and B) and a sum output (S). The input A and B can either be 0 or 1, and the sum output S is calculated based on the following truth table:

In a 1-bit adder, the sum output S is equal to the exclusive OR (XOR) of the two inputs A and B. The exclusive OR operation is a logical operation that returns a 1 if one of the inputs is 1 and the other is 0, and returns a 0 if both inputs are the same.

In a 4-bit parallel adder, the two input numbers are represented by four bits each, and the sum output is represented by a 5-bit number. The 4-bit parallel adder consists of four 1-bit adders, one for each bit of the input numbers. The sum output of each 1-bit adder is fed as an input to the next 1-bit adder, along with the carry-in bit (Cin) from the previous 1-bit adder. The carry-in bit represents the carry-over from the previous addition, which occurs when the sum output of a 1-bit adder is equal to 2 (i.e., 10 in binary).

The 4-bit parallel adder also includes a carry-out (Cout) bit, which is the carry-over from the addition of the most significant bit (MSB). The carry-out bit is important because it indicates when the sum of the two input numbers is greater than 15 (i.e., 1111 in binary), which is the maximum value that can be represented by a 4-bit number.

In summary, the 4-bit parallel adder is a digital circuit that is used to perform arithmetic operations, specifically addition, on two 4-bit binary numbers. It consists of four 1-bit adders, a carry-in bit, and a carry-out bit, and it performs the addition simultaneously on all the bits of the two input numbers. The 4-bit parallel adder is an important component in many digital systems and is widely used in computers and other electronic devices.

## Parallel Adder

So for the two-bit number, two adders are needed while for four bit number, four adders are needed and so on. The carry C1, C2 are serially passed to the successive full adder as one of the inputs. In this gate, if either of the inputs is low 0 , then the output is also low. An AND gate is a logic gate having two or more inputs and a single output. But this is usually overcome by using larger words. Also see : How to Design a 4 bit Magnitude Comparator Circuit? As the name implies, a four bit full adder can add four input bits. This is further added to A to carry out the arithmetic subtraction.

## Four Bit Adder Verilog Code

GlobalSpec may share your personal information and website activity with our clients for which you express explicit interest, or with vendors looking to reach people like you. The input of the Full Adder is the carry bit from the previous Full Adder. This circuit works using an EX-OR gate, binary addition and subtraction, Full adder. Periodically, these affiliates, editorial sponsors, and sponsored content providers will reach out to you via email to determine if you have additional interest in their product or service. In ordinary addition of binary numbers we use only two bits at a time in order to add them i. Parallel Subtractor — A Parallel Subtractor is a digital circuit capable of finding the arithmetic difference of two binary numbers that is greater than one bit in length by operating on corresponding pairs of bits in parallel. Full Adder is the adder which adds three inputs and produces two outputs.