MINI LESSON 5 – INTEGRATED CIRCUITS

 

 

“REAL” LOGIC GATES

 

  • We have looked at the theory of circuit diagrams using simple logic gates.  We will now step into the real world.

·        Simple logic gates are created as small integrated circuit chips that usually contain several gates.  Here is an image of such a chip:

  • Each chip type has a specific number.  For example, a 7400 chip holds NAND gates while a 7404 chip holds NOT gates.

CHIP PINOUTS

 

  • To use a chip, we need to know what each of its pins does.  In other words, we need to know how they are connected to the internal circuitry of the chip. 

  • The function of each pin for a specific chip is called the chip pinout.  It is usually represented in a diagram.

  • Here is a chip pinout diagram for the 7400 chip:

 

·        One can orient the chip based on the half circle (done in red) on the end of all chips.

·        Pins are numbered 1 to 14 (depending on the amount of pins) in the counter-clockwise direction starting at the half circle.  See below.

 

 

·        One aspect that is not considered in the previous circuit diagrams is the fact that the gates themselves need to be powered.  Two pins are used for this.  The last pin on the first side of the chip is usually GND and the last pin on the other side is usually V++.

 

·        The 7400 ICs are designed to function with a 5V power supply.

 

COMMON GATE NUMBERS

 

·        Here is a list of common gate numbers:

 

Number

Logic Gate Type

Number of Gates

Number of Inputs

per Gate

7400

NAND

4

2

7402

NOR

4

2

7404

NOT

6

1

7408

AND

4

2

7432

OR

4

2

7486

XOR

4

2

 

USING IC CIRCUITS

 

  • For a chip to work, it needs to be powered.

  • To provide an input of 1, we connect that pin to +5V.

  • To provide an input of 0, we connect that pin to ground (0V).  We cannot simply leave the pin unconnected.