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

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

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Step 3: Draw the Digital System Diagram : Group variables that are ANDed together into a single block. This block is called product term (P-Term). 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 (Q1, Q2, Q3). Dollar (L). Logic 1 = currency present. Outputs : Package (P). Quarter Change (C). Logic 1 = dispense item. Q3 Q2 Q1 L P C Step 2: Generate Equation for the system: Dispense Package if Quarter1 and Quarter2 and Quarter3 OR Dollar is inserted. Dispense change if dollar is inserted. P = Q1 Q2 Q3 + L C = L P-Term : thus : P = + L Work from output towards input. P must be connected to an OR gate. L = + L Re-insert the P-Term (Q1 Q2 Q3). A 3 input AND gate is required. Q1 Q2 Q3 Connect L to OR gate and connect C to L (C=L). Once the system diagram is complete it can be used to test the operation of the system. Here is what happens when someone inserts 3 quarters. 0 1 1 1 1 0 1 1 0 1 0 0 0 0 1 0 1 1 Here is what happens when someone inserts a dollar. 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? 0 1 0 0 0 0 0 0 0 The result: The package and the change would be dispensed. The un-happy user of the machine would have paid $1 ($1.25 - $0.25 change). To resolve this problem an extra change output could be added. 1 1 0 0 0 1 0 1 1 C2C2 1 1 1 Slide #3

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Lab 03 : Older Generation IC Technology : Older generation IC technology such as TTL ICs (transistor, transistor, logic) could often require students to interconnect 5 to 15 ICs. 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

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