2. Half Adder Logic Diagram Truth Table A half adder adds two one-bit binary numbers A and B . It has two outputs, S and C . The simplest half-adder design, pictured on the right, incorporates an XOR gate for S and an AND gate for C . Half adders cannot be used compositely, given their incapacity for a carry-in bit.
3. Full Adder A full adder adds binary numbers and accounts for values carried in as well as out. A one-bit full adder adds three one-bit numbers, often written as A , B , and C in ; A and B are the operands, and C in is a bit carried in. A full adder can be constructed from two half adders by connecting A and B to the input of one half adder, connecting the sum from that to an input to the second adder, connecting C in to the other input and OR the two carry outputs Logic Diagram Truth Table
4. SR Flip-Flop Graphic Symbol Truth Table A SR flip-flop has three inputs, S (for set ), R (for reset ) and C (for clock ). It has an output Q. The undefined condition makes the SR flip-flop difficult to manage and therefore it is seldom used in practice.
5. D Flip-Flop Graphic Symbol Truth Table The D flip-flop is a slight modification of the SR flip-flop by inserting an inverter between S and R and assigning the symbol D to the single input. If D=1, the output goes to the state 1, and if D=0, the output of the flip flop goes to the 0 state.
6. JK Flip-Flop Graphic Symbol Truth Table Inputs J and K behave like inputs S and R. When inputs J and K are both equal to 1, a clock transition switches the output of the flip-flop to their complement state.
7. T Flip-Flop Truth Table Graphic Symbol The T flip-flop is obtained from a JK flip-flop when inputs J and K are connected to provide a single input designated by T. The flip-flop thus has only two conditions.
8. Excitation Tables During the design of circuits, we need a table that lists the required input combinations for a given change of state. Such table is called a flip flop excitation table.
9. Sequential Circuits <ul><li>A sequential circuit is an interconnection of flip-flops and gates. </li></ul>Example of a Sequential Circuit Ax Bx Ax+Bx A’x x’ A+B (A+B).x A=Ax+Bx, B=A’x y=(A+B).x State Table