Lab 03 Vending Machine System Slide 2 Logic

Lab 03 : Vending Machine System : Slide #2 Logic Gate Equations: Slide #3 Vending Machine System: Slide #4 Older Generation IC Technology:

Lab 03 : Logic Gate Equations : Each logic gate has a Boolean equation to represent its operation. Input A NOT Output X Boolean Equation: Input A AND Output X Input B Input A Input B Slide #2 OR Boolean Equation: Output X

Lab 03 : Vending Machine System: Design a logic system for a vending machine that will dispense a 75 cent surprise gift package if any of the following conditions occur… Three quarters are inserted. A dollar is inserted. The machine can only accept quarters and a dollar coin / note. Step 1: Declare Inputs and Outputs: Inputs : Quarters (Q 1, Q 2, Q 3). Dollar (L). Logic 1 = currency present. Outputs : Package (P). Quarter Change (C). Logic 1 = dispense item. 1 Q 3 0 1 Q 2 0 0 Q 1 1 0 1 L 1 Q 1 • Q 2 • Q 3 0 0 1 L 1 0 0 1 P = +L 1 0 C 1 Step 2: Generate Equation for the system: 1 1 Dispense Package if Quarter 1 and Quarter 2 and Quarter 3 OR Dollar is inserted. Dispense change if dollar is inserted. C 2 Once the system diagram. P is=complete it can Q 1 • Q 2 • Q 3 be+used L to test the operation. Cof=the L system. Here is what happens when someone inserts 3 quarters. Here is what happens when someone inserts P-Term a dollar. : thus : P = + L Here is what happens when someone searches their pocket finds a quarter and inserts it into the machine. Then they realize that they do not have 2 more quarters! If they insert a dollar what would be the result? Step Draw thepackage Digital and System Diagram : be dispensed. The un-happy user of the machine would have paid The 3: result : The the change would $1 ($1. 25 - $0. 25 To resolve problem extra. This change output could be added. Group variables thatchange). are ANDed togetherthis into a singleanblock is called product term (P-Term). Work from output towards input. P must be connected to an OR gate. Slide #3 Re-insert the P-Term (Q 1 • Q 2 • Q 3). A 3 input AND gate is required. Connect L to OR gate and connect C to L (C=L).

Lab 03 : Older Generation IC Technology : Older generation IC technology such as TTL IC’s (transistor, logic) could often require students to interconnect 5 to 15 IC’s. The wiring would often be very complex and messy. Complex designs looked so messy that the term spaghetti factory was used to describe the appearance of the wiring. Slide #4