Chapter IV : Logic circuits

∗Logic circuits∗

Logic gates

A logic gate is a foundation of a digital circuit. It controls the flow of electronic signals either high voltage or low voltage . They represent components in a computer. Many electronic circuits operate using binary logic gates. They process signals which are true/false, on/off or 1/0. Truth tables are used to show the outcome of logic circuits.

---

---

The AND gate 
The output (x) will only be high voltage if both inputs (A and B) 
are high voltage. So if A & B are 1, X = 1 You can write logic 
statements (aka boolean statements) to represent a logic gate. 
X = A AND B or X = A.B (the . represents AND) 

---

The OR gate


The output (x) will be high voltage if A or B/ A and B input is 
high voltage. 

X = A OR B
or
X = A+B (the + represents OR)

---

The NOT gate


The output (x) will only be high voltage if the input is low voltage

X = NOT A
or 
X = Ā

---

The NOR gate (OR then NOT)


The output (x) will be high voltage if A and B input is low voltage.
So X will be 1 if A and B are not 1.

X = A NOR B
or
X = a + b
or
X = 

---

The XOR/EOR gate
 

The output (x) will be high voltage if A or B input is high voltage.
So X will be 1 or A or B are 1 but if A and B are 1, X will be 0.

X = A XOR B
or
X = (a.b) + (a.b)
or
X = 

---

The NAND gate (AND then NOT)


The output (x) will be low voltage if A and B input is high voltage. 
Output will be 1 unless A and B are 1.
NAND gates are special because its a universal logic that makes 
NAND gates an alternative to making other gates. 
 
X = A NAND B
or
X = a.b
or
X = 




NAND gates used to make other gates: