5/26/2019 0 Comments 4 Bit Arithmetic Logic UnitThe 74181 is a bit slice arithmetic logic unit (ALU), implemented as a 7400 series TTL integrated circuit.The first complete ALU on a single chip, it was used as the arithmetic/logic core in the CPUs of many historically significant minicomputers and other devices. May 26, 2017 - Reversible logic has received a great attention in the recent years due to its ability to reduce the power dissipation. The main purposes of. A symbolic representation of an ALU and its input and output signals, indicated by arrows pointing into or out of the ALU, respectively. Each arrow represents one or more signals. Control signals enter from the left and status signals exit on the right; data flows from top to bottom. An arithmetic logic unit ( ALU) is a that performs and on. Mac os 9.0.4 iso. This is in contrast to a (FPU), which operates on numbers. An ALU is a fundamental building block of many types of computing circuits, including the (CPU) of computers, FPUs, and (GPUs). A single CPU, FPU or GPU may contain multiple ALUs. The inputs to an ALU are the data to be operated on, called, and a code indicating the operation to be performed; the ALU's output is the result of the performed operation. In many designs, the ALU also has status inputs or outputs, or both, which convey information about a previous operation or the current operation, respectively, between the ALU and external. Contents • • • • • • • • • • • • • • • • • • • • Signals [ ] An ALU has a variety of input and output, which are the used to convey between the ALU and external circuitry. When an ALU is operating, external circuits apply signals to the ALU inputs and, in response, the ALU produces and conveys signals to external circuitry via its outputs. Data [ ] A basic ALU has three parallel data consisting of two input ( A and B) and a result output ( Y). Each data bus is a group of signals that conveys one binary integer number. Typically, the A, B and Y bus widths (the number of signals comprising each bus) are identical and match the native of the external circuitry (e.g., the encapsulating CPU or other processor). Opcode [ ] The opcode input is a parallel bus that conveys to the ALU an operation selection code, which is an enumerated value that specifies the desired arithmetic or logic operation to be performed by the ALU. The opcode size (its bus width) determines the maximum number of different operations the ALU can perform; for example, a four-bit opcode can specify up to sixteen different ALU operations. Generally, an ALU opcode is not the same as a, though in some cases it may be directly encoded as a bit field within a machine language opcode. Status [ ] Outputs [ ] The status outputs are various individual signals that convey supplemental information about the result of the current ALU operation. General-purpose ALUs commonly have status signals such as: • Carry-out, which conveys the resulting from an addition operation, the borrow resulting from a subtraction operation, or the overflow bit resulting from a binary shift operation. • Zero, which indicates all bits of Y are logic zero. • Negative, which indicates the result of an arithmetic operation is negative. •, which indicates the result of an arithmetic operation has exceeded the numeric range of Y. •, which indicates whether an even or odd number of bits in Y are logic one. At the end of each ALU operation, the status output signals are usually stored in external registers to make them available for future ALU operations (e.g., to implement ) or for controlling. The collection of bit registers that store the status outputs are often treated as a single, multi-bit register, which is referred to as the 'status register' or 'condition code register'. Inputs [ ] The status inputs allow additional information to be made available to the ALU when performing an operation. Typically, this is a single 'carry-in' bit that is the stored carry-out from a previous ALU operation. Circuit operation [ ]. The circuitry of the integrated circuit, which is a simple four-bit ALU An ALU is a circuit, meaning that its outputs will change asynchronously in response to input changes. In normal operation, stable signals are applied to all of the ALU inputs and, when enough time (known as the ') has passed for the signals to propagate through the ALU circuitry, the result of the ALU operation appears at the ALU outputs. The external circuitry connected to the ALU is responsible for ensuring the stability of ALU input signals throughout the operation, and for allowing sufficient time for the signals to propagate through the ALU before sampling the ALU result. In general, external circuitry controls an ALU by applying signals to its inputs.
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