LESSON3.docx

**COMBINATIONAL LOGIC CIRCUIT** **ERROR DETECTOR/ PARITY GENERATOR** **ADDER** - It is a digital logic circuit used for the addition of numbers and to calculate addresses and related activities. It is also used to calculate table indices in the ALU and even utilized in other parts o...

**COMBINATIONAL LOGIC CIRCUIT** **ERROR DETECTOR/ PARITY GENERATOR** **ADDER** - It is a digital logic circuit used for the addition of numbers and to calculate addresses and related activities. It is also used to calculate table indices in the ALU and even utilized in other parts of the processors. There are several kinds of adders. **HALF ADDER** - it is one of the most basic building blocks of calculator and computer circuit. Its function is to add two bits in binary fashion.  **FULL ADDER** - Its function is to perform the addition of 3 bits  **BINARY ADDER** - its function is to add two binary numbers not just bits. The most common size is to add two 4-bit binary numbers  **BCD ADDER** - it is used in adding BCD numbers because a simple binary adder cannot perform this task since the number in BCD code is only from 0-9 which is from 0000-1001. The number 10 in binary is 1010 while the number 10 in BCD form is 0001 0000 which is very different. We add BCD numbers in a binary way but if a group produces a carry or its sum is greater than 9, we have to add 6 (0110).   **SUBTRACTOR** - Subtraction of binary numbers cannot be directly implemented by logic gates, since we don't have a specific subtraction gate. Subtraction using complement notation is the most widely used method. **USING 1'S COMPLEMENT**   **USING 2'S COMPLEMENT**  **HALF SUBTRACTOR** - its function is to perform subtraction of 2 bits  **FULL SUBTRACTOR** - its function is to perform subtraction of 3 bits **COMPARATOR** - these are circuits that checks and compares two bits or sometimes two binary words. They use terms like equal, not equal, greater than, less than  **MULTIPLEXER** - These are data selector circuits that select one form many input lines through data select control bits. The data select input DS chooses which input (A or B) will transfer its data to the output. When DS is logic 1, the AND gate where input B is connected automatically produces a logic 0 output, and whatever data we introduce at input A, becomes the output data. The switch analogy shows clearly how DS controls what input line will transfer its data to the output.  **DEMULTIPLEXER** - It is also called the distributor circuit. It has only a single input line but a lot of output. Only one output will be enabled at a time that is that particular output will be equal to the input while the unselected output will remain at logic 0. An output can be selected using select input similar to a multiplexer.  **ENCODER** - It is a combinational circuit that produces a reverse output to that of a decoder. It has 2n input lines and 'n' output lines. It is categorized as lines to bits or bits code converters. These circuits are responsible for digital code conversions. They are required in digital and computer systems because there is a necessity in converting a human code form into binary code from or one binary code into another. - The encoder is a device or a transducer of a circuit. It will convert the information from one format to another format **DECODER** - It is a combinational circuit that converts the binary bit of 'n' input lines to a maximum of 2n output lines. Decoders are digital ICs which are used for decoding. It decrypts or obtain the actual data from the received code and can be used to obtain the required data from the code for obtaining the parallel data from the serial data received.  **BINARY CODE** - In the coding, when numbers, letters or words are represented by a specific group of symbols, it is said that the number, letter or word is being encoded. The group of symbols is called as a code. The digital data is represented, stored and transmitted as group of binary bits. This group is also called as binary code. The binary code is represented by the number as well as alphanumeric letter. **WEIGHTED CODES**  **BINARY CODE DECIMAL (BCD) CODE** **NON WEIGHTED CODE** - In this type of binary codes, the positional weights are not assigned. The examples of non-weighted codes are Excess-3 code and Gray code **EXCESS-3 CODE**  **GRAY CODE**  **APPLICATION OF GRAY CODE** - Gray code is popularly used in the shaft position encoders - A shaft position encoder produces a code word which represents the angular position of the shaft **CONVERSION**