Design a combinational logic circuit a Determine the input variables and output variables that are involved Problem statement Assign mnemonic or letter or number symbols to each variable a Determine the size of the truth Truth table table Construction Construct a truth table containing all of the input variable combination By careful reading of the problem statement determine the combinations of input that cause a given output to be true
Design a combinational logic circuit ◼ Determine the input variables and output variables that are involved ◼ Assign mnemonic or letter or number symbols to each variable ◼ Determine the size of the truth table ◼ Construct a truth table containing all of the input variable combination ◼ By careful reading of the problem statement determine the combinations of input that cause a given output to be true Truth table Construction Problem statement
Example Conveyor system 口 Elements a Two operator ■ Materia ■ Inter| ock switch ■ Motor a put conveyor into action >>the motor is turning on a Either of two operators is in position The interlock switch is closed a Material must be present
Elements ◼ Two operator ◼ Material ◼ Interlock switch ◼ Motor put conveyor into action >> the motor is turning on ◼ Either of two operators is in position ◼ The interlock switch is closed ◼ Material must be present Example : Conveyor system
Example: Conveyor system 4 input variables a=1, operator 1 is in position b=1, operator 2 is in position a m=1, material is present s=1. interlock switch is closed 口1 output variable aM is the signal to turn the motor off or on a M=1, the motor is turning on
4 input variables ◼ a=1, operator 1 is in position ◼ b=1, operator 2 is in position ◼ m=1, material is present ◼ s=1, interlock switch is closed. 1 output variable ◼ M is the signal to turn the motor off or on ◼ M=1, the motor is turning on Example : Conveyor system
Example: Conveyor system a bm s m a bms M 00000 10000 0001 0 10010 00100 1010 0 00 10111 00 11000 0000 01 00001 1 1 110 111 011 0 001
a b m s M 0 0 0 0 0 0 0 0 0 0 0 0 1 1 1 1 0 0 1 1 0 0 1 1 0 1 0 1 0 1 0 1 a b m s M 1 1 1 1 1 1 1 1 0 0 0 0 1 1 1 1 0 0 1 1 0 0 1 1 0 1 0 1 0 1 0 1 0 0 0 0 0 0 0 1 0 0 0 1 0 0 0 1 Example : Conveyor system
Example: Nasn syStem a Elements Two on-line computers a One redundant computer a Three self-checking diagnostics components a The control logic to connect or disconnect the computers A warning allow the third computer to come on-line aa warning invoke the emergency procedures
Elements ◼ Two on-line computers ◼ One redundant computer ◼ Three self-checking diagnostics components ◼ The control logic to connect or disconnect the computers. ◼ A warning, allow the third computer to come on-line. ◼ A warning, invoke the emergency procedures. Example : NASN system