Bit serial adder

Whenever the value of one of the signals in the sensitivity list changes, the process is executed. For example, " process CLK " means that whenever the clock signal "CLK" changes it can be both rising and falling edge , the process is executed. If-then-else statements can be used only within the process statements. Using if-then-else statements outside the process will yield an error. Positive-edge-triggered D-type flip-flop is implemented by checking the rising edge of the clock signal using if-then-else statement.

A typical implementation of the D-type flip-flop is given below:. There is a big difference between a signal and a variable. A variable is defined in the beginning of the process and has an immediate behavior. The assignment of the value to the variable occurs immediately with no delay:.

Signal on the other hand can be considered as a flip-flop or a register. The assignment of the value to the signal i.

After checking the pinouts of the circuit in the floorplan area or by editing the UCF-file which is given in "Basys2. Press on the "Generate Programming File" button. If the compilation process ends successfully, flash the Basys2 board with the generated bit-file using Adept program. To test the circuit, firstly turn on and off proper switches which set numbers A and B. Then press on the "Load" button and keep holding.

Change Language. Related Articles. Table of Contents. Improve Article. Save Article. Like Article. Recommended Articles. Article Contributed By :. Each D Flip Flop of the input registers has a corresponding multiplexer used to choose between loading data parallelly to them or shifting right by 1 bit. The output sum register however does not need any of this and hence, the outputs of each D Flip Flop is directly fed as input to the next one.

Since addition takes place in a serial fashion, this adder takes n-cycles to add two n-bit numbers. In this implementation, n is 16 and hence this adder takes 16 cycles to compute the sum of two 16 bit numbers.

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