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4 bit binary Adder introduction:-

Binary adders are implemented to add two binary numbers. So in order to add two 4 bit binary numbers we need to use 4 full-adders. The connection of full-adders to create bianry adder circuit is discussed in block diagram below.

In this implementation, carry of each full-adder is connected to previous carry. Detailed discussion on full-adder is covered on this link.

In this implementation, carry of each full-

Example

Lets discuss one example for 4 bit binary Adder. In this example we will use some terms from Register Transfer Level (RTL) implementations.

Q. Add two binary numbers 7 and 15 with previous carry = 0.

Sol. Load the values in two registers R1 and R2.

So, R1 = 7 (decimal) = 0111 (in binary A3A2A1A0)

& R2 = 15 (decimal) = 1111 (in binary B3B2B1B0)

So from the above implementation we have -

Lets discuss one example for 4 bit binary Adder. In this example we will use some terms from Register Transfer Level (RTL) implementations.

Q. Add two binary numbers 7 and 15 with previous carry = 0.

Sol. Load the values in two registers R1 and R2.

So, R1 = 7 (decimal) = 0111 (in binary A3A2A1A0)

& R2 = 15 (decimal) = 1111 (in binary B3B2B1B0)

So from the above implementation we have -

Stage

Previous carry

Augends bits A

Addend bits B

Sum

Next carry

0

C0=0

A0=1

B0=1

S0=0

C1=1

1

C1=1

A1=1

B1=1

S1=1

C2=1

2

C2=1

A2=1

B2=1

S2=1

C3=1

3

C3=1

A3=0

B3=1

S3=0

C4=1

Sum of two binary numbers 7 and 15 from above table

Is C4S3S2S1S0 = 10110 (In Binary) = 16 (decimal)

Is C4S3S2S1S0 = 10110 (In Binary) = 16 (decimal)

In the results we have appended C4 in front of the sum digits to accommodate overflow bit from the binary addition flow. Overflow is discussed in this section.

Half-Adder , Full-Adder , Adder-Subtractor .

Verilog code - Half-Adder , Full-Adder

Verilog code -

Resources

Digital design resources

Clock Domain Crossing rtl & testbench.

Rate change (asynchronous) FIFO design and fifo depth calculation.

Half-adder , Full-adder , 4-bit binary adder , adder-subtractor circuit, overflow with rtl & testbench. Binary Multiplier, Parity error TT, Arithmetic, logical, shift micro-operations . Stack organization, LIFO, RPN discussion.

RTL coding guidelines. ICG cell, Assertions, $assertkill, levels.

Digital design Interview questions.

FPGA Interview. FPGA flow.

Guide to Graduate studies in US

Pipeline vs. Parallel processing.

Digital design resources

Clock Domain Crossing rtl & testbench.

Rate change (asynchronous) FIFO design and fifo depth calculation.

Half-

Digital design Interview questions.

FPGA Interview. FPGA flow.

Guide to Graduate studies in US

Pipeline vs. Parallel processing.