Arithmetic logic unit Wikipedia. A symbolic representation of an ALU and its input and output signals, indicated by arrows pointing into or out of the ALU, respectively. Up And Down The River Card Game Score Sheet more. 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 combinationaldigital electronic circuit that performs arithmetic and bitwise operations on integerbinary numbers. This is in contrast to a floating point unit FPU, which operates on floating point numbers. An ALU is a fundamental building block of many types of computing circuits, including the central processing unit CPU of computers, FPUs, and graphics processing units GPUs. A single CPU, FPU or GPU may contain multiple ALUs. The inputs to an ALU are the data to be operated on, called operands, and a code indicating the operation to be performed the ALUs 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 status registers. Express Helpline Get answer of your question fast from real experts. Hi, anyone has CAN interview question related docs or website. Please post it. Next week I have 23 interviews related to automotive. SignalseditAn ALU has a variety of input and output nets, which are the electrical conductors used to convey digital signals 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. A basic ALU has three parallel data buses consisting of two input operands 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 word size of the external circuitry e. Kilauea Mount Etna Mount Yasur Mount Nyiragongo and Nyamuragira Piton de la Fournaise Erta Ale. CPU or other processor. 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 machine language opcode, though in some cases it may be directly encoded as a bit field within a machine language opcode. No more missed important software updates UpdateStar 11 lets you stay up to date and secure with the software on your computer. Serial Multiplier Vhdl Code Examples' title='Serial Multiplier Vhdl Code Examples' />OutputseditThe 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 carry 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. Overflow, which indicates the result of an arithmetic operation has exceeded the numeric range of Y. Parity, 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. 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. 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 operationeditAn ALU is a combinational logic 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 propagation delay 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. Typically, the external circuitry employs sequential logic to control the ALU operation, which is paced by a clock signal of a sufficiently low frequency to ensure enough time for the ALU outputs to settle under worst case conditions. For example, a CPU begins an ALU addition operation by routing operands from their sources which are usually registers to the ALUs operand inputs, while the control unit simultaneously applies a value to the ALUs opcode input, configuring it to perform addition. At the same time, the CPU also routes the ALU result output to a destination register that will receive the sum. The ALUs input signals, which are held stable until the next clock, are allowed to propagate through the ALU and to the destination register while the CPU waits for the next clock. When the next clock arrives, the destination register stores the ALU result and, since the ALU operation has completed, the ALU inputs may be set up for the next ALU operation. FunctionseditA number of basic arithmetic and bitwise logic functions are commonly supported by ALUs. Basic, general purpose ALUs typically include these operations in their repertoires Arithmetic operationseditAdd A and B are summed and the sum appears at Y and carry out. Add with carry A, B and carry in are summed and the sum appears at Y and carry out. Subtract B is subtracted from A or vice versa and the difference appears at Y and carry out. For this function, carry out is effectively a borrow indicator. This operation may also be used to compare the magnitudes of A and B in such cases the Y output may be ignored by the processor, which is only interested in the status bits particularly zero and negative that result from the operation. Subtract with borrow B is subtracted from A or vice versa with borrow carry in and the difference appears at Y and carry out borrow out. Twos complement negate A or B is subtracted from zero and the difference appears at Y. Increment A or B is increased by one and the resulting value appears at Y. Decrement A or B is decreased by one and the resulting value appears at Y. Pass through all bits of A or B appear unmodified at Y. This operation is typically used to determine the parity of the operand or whether it is zero or negative, or to load the operand into a processor register. Bitwise logical operationseditAND the bitwise AND of A and B appears at Y. OR the bitwise OR of A and B appears at Y. Exclusive OR the bitwise XOR of A and B appears at Y. Ones complement all bits of A or B are inverted and appear at Y. Bit shift operationseditALU shift operations cause operand A or B to shift left or right depending on the opcode and the shifted operand appears at Y. Simple ALUs typically can shift the operand by only one bit position, whereas more complex ALUs employ barrel shifters that allow them to shift the operand by an arbitrary number of bits in one operation.