EC2.101 - Digital Systems and Microcontrollers | DSM Lecture 5

with Prof. Aftab Hussain, Prof. Harikumar
Mar 01, 2020 - Sunday
Written by: Pratyaksh Gautam

Logic Gates

We represent binary signals in digital systems as high voltage (1), and low voltage (0) signals. For example, Arduino reads 3-5V as HIGH, or true and 0.-1.5V as LOW or false.
Note: Other than NOT gate, logic gates can have more than two inputs

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Boolean Functions

A boolean function described by a boolean expression has binary variables, and constants 0, and 1, and logic operation symbols. The function must return a value of either 0, or 1. eg. $F = x + y.z$

Boolean functions can be represented as a truth table, and the number of rows is given by $2^n$, where n is the number of variables in the function. For each boolean function we have one, and only one, truth table. Multiple algebraic forms may have the same truth table; in that case they are equivalent statements or functions.

By manipulating a boolean expression according to the rules of boolean algebra, it is sometimes possible to obtain simpler expressions, reducing the complexity of the circuit representing it.

Complement of a function

The complement of a function F is the function such that it outputs 0 when F outputs 1, and vice versa. We can also derive the complement algebraically:

$$ \begin{align} F &= x + y'z \ \Rightarrow F' &= x'.(y'z)' \ &= x'.(y + z') \ \end{align} $$

The generalized form of DeMorgan’s theorem states that you can

Minterms

A minterm is a standard product, for $n$ binary variables, we can have $2^n$ possible minterms.
For eg. with variables x and y

| x | y | $m_i$ | |---|---| --- | | 0 | 0 | $m_0: x'y'$| | 0 | 1 | $m_1: x'y$ | | 1 | 0 | $m_2: x'y$ | | 1 | 1 | $m_3: xy$ |

Maxterms

Similarly we have maxterms, which are standard sums.
For eg. with variables x and y

| x | y | $M_i$ | |---|---| --- | | 0 | 0 | $M_0: x + y$ | | 0 | 1 | $M_1: x + y'$ | | 1 | 0 | $M_2: x' + y$ | | 1 | 1 | $M_3: x' + y'$ |