Intro to Digital Logic

What does Digital mean? A method of storing, processing and transmitting information through the use of distinct electronic or optical pulses that typically represent the binary digits 0 and 1. This is typically represented by transistors switched on or off Data carrying signals carry one of two possible values. 1/0,on/off,high/low, or pulse present/pulse absent

What was the earliest digital communication? Morse code? Does it have different states? 5 different states, but still digital Semaphore? What about smoke signals? One if by air, two if by sea? All digital, as they are using a code to represent a message

Logic! Why is this unit called digital logic? What is logic? Logic in these gates is based on theories from a book called An investigation in the laws of thought by George Boole. This came to be known as Boolean Logic or Boolean Algebra

Thoughts There IS a transition between the low and high, and back to low signals. In the ideal setting, there would be no transition. Real world circuits approximate this well enough that we will not take it into consideration

Gates There are seven gates. The first two are AND and OR gates

AND gate The AND gate logic is such that BOTH outputs must be high to trigger a high output This is like two doors in a row that both must be open to pass a beam of light through

The switch analogy We can build a manual approximation of the circuit using switches very easily.

The OR gate The OR gate is such that when a high signal is sent on either input, the output will be high. This is like a double door that either side can open to let the light through.

The switch analogy We can build a manual approximation of the circuit using switches very easily.

Positive Logic Vs Negative Logic

Positive Logic Vs. Negative Logic When describing the input states, we can use positive or negative logic For example, the AND gate: Positive Logic When both inputs are high, the output is high Negative Logic When either input is low, the output is low

Interesting coincidence On the and gate: If either input 1 OR input 2 are low, the output is low OR? How did OR get in there? This Positive AND gate is also a Negative OR gate! On an OR gate, both input 1 AND input 2 have to be low in order to have a low output! AND!? A positive OR gate is a Negative AND gate!

Truth Table (or trooth, if you rather) A truth table is helpful in determining what type of gate you have, or what you should expect based on your gate A and B represent the two inputs C represents output What type of gate is this?

Lab Time

Materials Power Supply (Use +5V DC) Digital Display Module Bread Board Interface Module 2 Data Switches Quad AND Gate Quad OR Gate Ribbon Cable Power Supply Leads Wire

How to set it up Plug the AND gates and Data switches together so they share a common strip in between. Plug in the Interface Module 2 in above the 2 other modules. Run a ground wire from the ground side of the AND gate to the ground on the Interface Module. Plug on end of the ribbon cable into the Interface Module and the other into the DDM on J2 Turn on power supply and set to +5v DC and hook the leads to the + and – side of the circuit.

Build a Single AND Gate Build a truth table for this circuit

Build a two AND Gate Circuit Build a truth table for this circuit

Build a three AND Gate Circuit Build a truth table for this circuit

Build a Single OR Gate Build a truth table for this circuit

Build a two OR Gate Circuit Build a truth table for this circuit

Build a circuit with one AND and one OR Build a truth table for this circuit