Let us learn about various combinational circuits – half-adder, full-adder, half-subtractor, full-subtractor, N-bit parallel adder, N-bit parallel subtractor etc that are generally part of an ALU. The semiconductor adder circuits can perform addition in a time less than 1 microseconds. The adder circuits are built by logic gates and flip-flops. The basic building blocks of the ALU are adders. A binary number may be available to the ALU of a digital processor either as parallel 8-bit, 16-bit, 32-bit or 64-bit input depending upon if it is 8-bit, 16-bit, 32-bit or 64-bit processor. So, ALU can perform arithmetic operations like addition and subtraction, and so multiplication and division on integer binary numbers. The ALU is typically designed to perform the following operations:ġ) Arithmetic Operations – Generally, the arithmetic operations supported by the ALU are addition, addition with carry, subtraction, subtraction with borrow, two’s complement, increment, decrement and pass through.Ģ) Bitwise Logical Operations – The logical operations supported by the ALU are AND, OR, Exclusive-OR and One’s Complement.ģ) Bit Shift Operations – The bit shift operations implemented in an ALU include arithmetic shift, logical shift, rotate and rotate through carry. The ALU are built by combinational circuits. In sequential circuits, the output depends not only on the present input but also past output values. In a combinational circuit, the output of the circuit depends only on the input values at that time. The digital circuits can be either of the two types – 1) Combinational Logic Circuits or 2) Sequential Logic Circuits. Within a Central Processing Unit (CPU) or Graphics Processing Unit (GPU) of a computer/computing device, there are many ALU and/or FPU (where FPU themselves are built from multiple ALU). A Floating Point Unit itself is built from multiple ALUs. In a processor/controller/ASIC, the arithmetic operations on integer binary numbers are performed by Arithmetic Logic Unit (ALU) while arithmetic operations on floating point numbers are performed by Floating Point Unit (FPU). The implementation of arithmetic operations by digital circuitry is further used to build up complex computing logics and mathematical functions. As a computing device, the digital circuitry of a processor, controller or ASIC must be essentially able to perform arithmetic operations. The digital circuits in general always have application as computing devices either as processor, controller or application specific ICs. The previous tutorials laid the foundation for logic synthesis and design of digital circuits.
0 Comments
Leave a Reply. |
AuthorWrite something about yourself. No need to be fancy, just an overview. ArchivesCategories |