Digital Logic Computer Science Department, niversity of …数字逻辑，计算机科学系，大学….pptVIP

Digital Logic ENEL 111 Digital systems A digital system is a system whose inputs and outputs fall within a discrete, finite set of values Two main types Combinational Outputs dependent only on current input Sequential Outputs dependent on both past and present inputs Combinational Logic Circuits Aims To express the inputs and outputs of a system in binary form To develop the relationships between these inputs and outputs as a truth table To simplify the Boolean expression using algebra or Karnaugh maps To select suitable electronic devices to implement the required function Example Consider a buzzer which sounds when : The lights are on and The door is open and No key is in the ignition Example Truth Table A Truth Table can be used to show the relationships between : the 3 inputs and the single output Implementation as a circuit using logic gates Summary Inputs and Outputs are expressed in Binary Form A truth table showing relationships between inputs and outputs is constructed A circuit is built to implement the circuit This lecture Truth tables for primitive functions Boolean notation Sum of products Boolean algebra Truth Tables and Boolean Notation Circuits with one input Buffer P = A Not P = A Basic AND / OR Circuits with two Inputs AND P = A.B OR P=A+B Basic NAND / NOR Problems with two Inputs NAND P = A.B NOR P=A+B Basic XOR / XNOR Circuits with two Inputs: XOR P = A ? B XNOR P = A ? B Primitive gates All circuits can actually be made using AND, OR and NOT gates if required. Exercise Not Symbol You should be aware that Combinational Logic Circuits Reminder from our overview To express the inputs and outputs of a system in binary form To develop the relationships between these inputs and outputs as a truth table To simplify the Boolean expression using algebra or Karnaugh maps To select suitable electronic devices to implement the required function Our Example Consider a buzzer which sounds when : The lights are on and