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Electronic Logic Conventions
Electronic logic conventions are the sets of rules followed while designing a digital logic system or device. These conventions are adopted due to their different characteristics observed by several experiments. The use of electronic logic conventions, makes the implementation process of a digit system easy and smooth. Also, a standardization is achieved in the design. This tutorial is entirely meant for explaining different electronic logic conventions used in digital system implementations.
As we know, the digital systems are implemented in binary number system due to some technical and economic reasons. The binary number system follows Boolean’s rules to perform arithmetic operations such as addition, subtraction, multiplication, division, etc. Therefore, it is called Boolean algebra. The Boolean algebra is the basis of electronic logic conventions.
In Boolean algebra, we uses the values 0 and 1 to represent the two values of a Boolean variables. Where, 0 is used to represent the LOW or FALSE state of a Boolean variable. While, the value 1 is used to represent the HIGH or TRUE state of a Boolean variable. In digital system designs, we use 0 and 1 to the represent two different states (LOW and HIGH respectively). This is because, this terminology is independent of the language. But, in English language, we prefer either LOW and HIGH or FALSE or TRUE to denote 0 and 1 respectively.
Types of Logic Conventions
In digital system implementation, there are two types of electronic logic conventions are to be followed, which are −
Positive Logic Convention
Negative Logic Convention
In digital logic system, it is almost universally followed that the binary value 0 is equivalent to FALSE, and the binary value 1 is equivalent to TRUE. Also, in terms of digital electronics, the meaning of 0 and 1 or LOW and HIGH is very concrete that the LOW (0) state represents the lower voltage levels and the HIGH (1) state represents the higher voltage levels. Therefore, we can use these value to describe the behavior of a digital electronic device without considering the actual voltage value.
Now, let us understand the meaning of the positive logic convention and negative logic convention individually.
Positive Logic Convention represents the higher voltage level by 1 or TRUE, and the low voltage level by 0 or FALSE.
On the other hand, Negative Logic Convention represents the higher voltage level by 0 or FALSE, and the lower voltage level by 1 or TRUE.
It is important to note that there is no any other logic convention other than these two, used in electronics. Also, we never use terms YES and NO to represents the states of a Boolean variable. However, sometime we might confused about ON and OFF, basically these terms are mainly used to represent the physical states of a system, and not the logical state.
Effect of Electronic Logic Conventions
Electronic logic convention is chosen before the implementation of a digital electronic device. Because, the alternative use of logic conventions can result in different output from a device. Now, let us understand the effect of electronic logic conventions on a two input AND gate.
If we first consider the positive logic convention, i.e. if the AND gate is implemented according to the positive logic convention, then it will produce a logic 1 or TRUE output when both of its inputs are logic 1 or TRUE. But, the output of the AND gate will become logic 0 or FALSE, if any one of its inputs or both inputs are 0 or FALSE.
On the hand, if the AND gate is implemented in the negative logic convention, then the output of the AND gate will be 1 or TRUE, when any one of its inputs or both inputs are 0 or FALSE. The output of the AND gate will be 0 or FALSE, if both of its inputs are 1 or TRUE.
Now, from this example, we can conclude that any Boolean function F1 that depends on a number of arguments has a related Boolean function F2, this function F2 is called the dual of the function F1 and is obtained from the function F1. The dual function F2 is basically the logical negation of the function F1 when its arguments are also negated. The dual relationship is symmetrical, which means if function F2 is a dual of the function F1, then F1 is also the dual of the function F2.
In this tutorial, we discussed the electronic logic conventions used in electronic industries. As we already discussed, there are two electronic logic conventions namely positive convention and negative convention, widely used to develop different electronic logic systems.
A logic device implemented in one convention (say positive convention) will show the dual function, i.e. negated function, in the other convention (or negative convention). However, the positive logic convention most extensively used because of its straight relationship between input and output which creates less confusion in implementation. But, the negative convention is also used, although it causes a great confusion. The main reason behind the use of negative convention perhaps is historical.
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