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VHDL stands for V ery high speed integrated circuit H ardware D escriptive L anguage. VHDL is a hardware descriptive language used to describe the behavior and structure of a digital system. Entity specifies the input and output of a particular device. Primary constants: Entity declaration. architecture body configuration declaration package declaration package body Rules: It is case insensitive. ex: a and A mean the same. half_adder and Half_ADDER are same. File name should always start with a alphabet '_' and other special characters can be used in file names The declaration include name,type of input and output. Entity declaration: Lets take an example, of half adder. sum is given by a xor b. and carry is given by a*b. entity declaration starts with the keyword entity. port is a keyword to specify input and output. input and output is represented as in bit or out bit. here bit is used to specify that it is one bit of informatio

Combinational logic circuits Sequential logic circuits          These are the basic building blocks of Logic Gates              These are the basic building blocks of Memory elements           The present output state depends only on the present input.  The present output depends on the                    Present input and also the previous output.               No clock is present Clock is present               Examples: Adders Substractors Multiplexers Encoders           Examples: Flip – Flops Registers Counters

RISC : Reduced Instruction Set Computer CISC : Complex Instruction Set Computer RISC Faster execution. single clock cycle execution few power-full instructions highly pipe-lined super scalar architecture hard wired control unit complex operation to software more coding CISC slow execution Rich and varied variety of power-full instruction. variable instruction format micro-programmed control unit external unit for accelerating computation easy to modify instruction set by modifying Micro-programmed control unit decreases software design complexity  less coding

Microprocessor is like a human brain. It can process information. whereas, Microconroller is like a human body which has brain, heart, lungs...etc. It goes without saying that microprocessors require external peripherals to function. Microprocessors Microprocessors are used for general purpose. i.e PC. which is flexible and meets wide-range of end user requirements. No external Interface ports are present. (I/O ports). There is no in-built memory.(RAM,ROM) I/O ports must be interfaced externally. Microcontrollers Microcontrollers are embedded systems. They perform a specific task over and over again. It is not flexible. They have in-built input and output ports. Memory is present. A finite amount of RAM and ROM is present in the microcontroller itself. Microcontrollers have inbuilt Timers and counters