Basic Electricity and Electronics Module Three Microprocessor Basics Copyright © Texas Education Agency, All rights reserved.

Digital Logic Digital logic is used for circuit design Digital logic is used for circuit design Also used for mathematical operations Also used for mathematical operations Called “Boolean Algebra” Called “Boolean Algebra” There are 7 total logic gates There are 7 total logic gates AND, OR, NOT, NAND, NOR, Exclusive-OR, Exclusive-NOR AND, OR, NOT, NAND, NOR, Exclusive-OR, Exclusive-NOR These gates are the building blocks for computers These gates are the building blocks for computers Copyright © Texas Education Agency, All rights reserved.

An Inverter - NOT gate Lets go back to our first transistor circuit: Lets go back to our first transistor circuit: V I = 0, the transistor is off, V O = V CC (+ 5 V) V I = 1, the transistor is on, V O = 0 (ground) V CC (+5v) VOVO VIVI Ground(0v) RCRC Copyright © Texas Education Agency, All rights reserved. Schematic symbol AQ 0110

A non-Inverter (does not change anything) VIVI V CC RERE Don’t like the inverter? Here is a circuit that does not invert Copyright © Texas Education Agency, All rights reserved.

We have established the concept that voltage turns on or off transistors We have established the concept that voltage turns on or off transistors We use transistors to make the circuits that do what we need We use transistors to make the circuits that do what we need Copyright © Texas Education Agency, All rights reserved.

The OR gate When ANY input is high, the output goes high When ANY input is high, the output goes high Does not perfectly match what we need, but gives us a starting point Does not perfectly match what we need, but gives us a starting point A B If EITHER input goes high, the transistor turns on This is called an OR gate Copyright © Texas Education Agency, All rights reserved.

This circuit works better This circuit works better The diodes protect one input from the other The diodes protect one input from the other The resistor limits current The resistor limits current A B Copyright © Texas Education Agency, All rights reserved.

Truth Table The truth table for the OR gate: The truth table for the OR gate: When ANY input is high, the output is high When ANY input is high, the output is high A B Q ABQ Schematic symbol (Or X) Copyright © Texas Education Agency, All rights reserved.

The AND Gate When BOTH inputs are high, we produce a carry When BOTH inputs are high, we produce a carry We need a circuit that will turn on only when both inputs are on We need a circuit that will turn on only when both inputs are on ABQ RERE B V CC A Q Schematic symbol Copyright © Texas Education Agency, All rights reserved.

Schematic Symbols We have seen the schematic symbols for 2 gates: We have seen the schematic symbols for 2 gates: AND Gate AND Gate OR Gate OR Gate Here is the schematic symbol for the inverter: Here is the schematic symbol for the inverter: NOT Gate NOT Gate With these three gates, you can make any logic circuit! With these three gates, you can make any logic circuit! Copyright © Texas Education Agency, All rights reserved.

Back to the Adder Here is how we make a binary adder: Here is how we make a binary adder: All circuits are made physically with transistors, but represented by symbols All circuits are made physically with transistors, but represented by symbols A B Σ (sum) C O (carry)ABΣ CoCoCoCo Copyright © Texas Education Agency, All rights reserved.

Back to the Adder Here is how we make a binary adder: Here is how we make a binary adder: All circuits are made physically with transistors, but represented by symbols All circuits are made physically with transistors, but represented by symbols A B Σ (sum) C O (carry)ABΣ CoCoCoCo Copyright © Texas Education Agency, All rights reserved.

Back to the Adder Here is how we make a binary adder: Here is how we make a binary adder: All circuits are made physically with transistors, but represented by symbols All circuits are made physically with transistors, but represented by symbols A B Σ (sum) C O (carry)ABΣ CoCoCoCo Copyright © Texas Education Agency, All rights reserved.

Back to the Adder Here is how we make a binary adder: Here is how we make a binary adder: All circuits are made physically with transistors, but represented by symbols All circuits are made physically with transistors, but represented by symbols A B Σ (sum) C O (carry)ABΣ CoCoCoCo Copyright © Texas Education Agency, All rights reserved.

Logic Circuit Applications A memory decoder A memory decoder A memory address is a unique number A memory address is a unique number Most logic circuits are simple, as this example shows Most logic circuits are simple, as this example shows A 2-bit code unlocks one of 4 memory locations when D goes high A 4-bit code would unlock one of 16 memory locations when D goes high Copyright © Texas Education Agency, All rights reserved.

3 Bit Decoder Any 3 bit binary number enables one AND gate Any 3 bit binary number enables one AND gate A0A0 A1A1 A2A2 D 0 = 1 (0 0 0) D 1 = 1 (0 0 1) D 3 = 1 (0 1 1) D 2 = 1 (0 1 0) D 4 = 1 (1 0 0) D 5 = 1 (1 0 1) D 6 = 1 (1 1 0) D 7 = 1 (1 1 1) Copyright © Texas Education Agency, All rights reserved. A0A1A2A0A1A2

A0A0 A1A1 A2A2 A3A3 A4A4 A5A5 765BA A3A 3B3B 3C3C 3D3D 3E3E 3F3F F2F 2E2E 2D2D 2C2C 2B2B 2A2A B1B 1A1A D1D C1C C E1E 1F1F FE1717 D 6 address lines, 16 AND gates and 6 inverters enable 64 memory locations

Computer Basics A computer uses voltage on wires to communicate A computer uses voltage on wires to communicate Communication involves data, addresses, and instructions Communication involves data, addresses, and instructions Each of these are represented by binary numbers in a code Each of these are represented by binary numbers in a code A logic circuit similar to what we have just seen is used to decode each of these A logic circuit similar to what we have just seen is used to decode each of these Copyright © Texas Education Agency, All rights reserved.

Bill Gates -1 st Personal Computer Watch video on how the 1 st personal computer worked HERE. Watch video on how the 1 st personal computer worked HERE.HERE Copyright © Texas Education Agency, All rights reserved.