Contains A Control Unit And An Arithmetic Logic Unit PdfBy Jade M. In and pdf 20.04.2021 at 04:02 4 min read
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- Arithmetic Logic Unit
- Arithmetic and Logical Unit ALU
- Computer - CPU(Central Processing Unit)
- 5 Difference Between Arithmetic Logical Unit (ALU) And Control Unit (CU)
Arithmetic Logic Unit
Reading Assignments and Exercises This section is organized as follows: 4. The Central Processor - Control and Dataflow 4. Datapath Design and Implementation 4. Single-Cycle and Multicycle Datapaths 4. Controller Finite State Machines 4. Microprogrammed Control Information contained herein was compiled from a variety of text- and Web-based sources, is intended as a teaching aid only to be used in conjunction with the required text , and is not to be used for any commercial purpose.
Particular thanks is given to Dr. Enrique Mafla for his permission to use selected illustrations from his course notes in these Web pages.
The Central Processor - Control and Dataflow Reading Assignments and Exercises Recall that, in Section 3, we designed an ALU based on a building blocks such as multiplexers for selecting an operation to produce ALU output, b carry lookahead adders to reduce the complexity and in practice the critical pathlength of arithmetic operations, and c components such as coprocessors to perform costly operations such as floating point arithmetic.
We also showed that computer arithmetic suffers from errors due to fintie precision, lack of associativity, and limitations of protocols such as the IEEE floating point standard. Review In previous sections, we discussed computer organization at the microarchitectural level, processor organization in terms of datapath, control, and register file , as well as logic circuits including clocking methodologies and sequential circuits such as latches.
In Figure 4. The fact that these are parallel buses is denoted by the slash through each line that signifies a bus. Figure 4. Schematic diagram of a modern von Neumann processor, where the CPU is denoted by a shaded box -adapted from [Maf01]. It is worthwhile to further discuss the following components in Figure 4. Datapath is the hardware that performs all the required operations, for example, ALU, registers, and internal buses.
Control is the hardware that tells the datapath what to do, in terms of switching, operation selection, data movement between ALU components, etc. The processor represented by the shaded block in Figure 4. Schematic diagram of the processor in Figure 4.
For example, implementational strategies and goals affect clock rate and CPI. These implementational constraints cause parameters of the components in Figure 4.
Such implementational concerns are reflected in the use of logic elements and clocking strategies. For example, with combinational elements such as adders, multiplexers, or shifters, outputs depend only on current inputs.
However, sequential elements such as memory and registers contain state information, and their output thus depends on their inputs data values and clock as well as on the stored state. The clock determines the order of events within a gate, and defines when signals can be converted to data to be read or written to processor components e. For purposes of review, the following diagram of clocking is presented:. Here, a signal that is held at logic high value is said to be asserted. In Section 1, we discussed how edge-triggered clocking can support a precise state transition on the active clock pulse edge either the rising or falling edge, depending on what the designer selects.
We also reviewed the SR Latch based on nor logic, and showed how this could be converted to a clocked SR latch. From this, a clocked D Latch and the D flip-flop were derived.
In particular, the D flip-flop has a falling-edge trigger, and its output is initially deasserted i. Register File The register file RF is a hardware device that has two read ports and one write port corresponding to the two inputs and one output of the ALU. The RF is comprised of a set of registers that can be read or written by supplying a register number to be accessed, as well in the case of write operations as a write authorization bit.
A block diagram of the RF is shown in Figure 4. Register file a block diagram, b implementation of two read ports, and c implementation of write port - adapted from [Maf01].
Since reading of a register-stored value does not change the state of the register, no "safety mechanism" is needed to prevent inadvertent overwriting of stored data, and we need only supply the register number to obtain the data stored in that register. This data is available at the Read Data output in Figure 4. However, when writing to a register, we need 1 a register number, 2 an authorization bit, for safety because the previous contents of the register selected for writing are overwritten by the write operation , and 3 a clock pulse that controls writing of data into the register.
In this discussion and throughout this section, we will assume that the register file is structured as shown in Figure 4. We further assume that each register is constructed from a linear array of D flip-flops, where each flip-flop has a clock C and data D input. The read ports can be implemented using two multiplexers, each having log 2 N control lines, where N is the number of bits in each register of the RF.
Similar to the ALU design presented in Section 3, parallelism is exploited for speed and simplicity. Here, the write enable signal is a clock pulse that activates the edge-triggered D flip-flops which comprise each register shown as a rectangle with clock C and data D inputs. The register number is input to an N-to-2 N decoder, and acts as the control signal to switch the data stream input into the Register Data input.
We next discuss how to construct a datapath from a register file and an ALU, among other components. Datapath Design and Implementation Reading Assignments and Exercises The datapath is the "brawn" of a processor, since it implements the fetch-decode-execute cycle. The general discipline for datapath design is to 1 determine the instruction classes and formats in the ISA, 2 design datapath components and interconnections for each instruction class or format, and 3 compose the datapath segments designed in Step 2 to yield a composite datapath.
Simple datapath components include memory stores the current instruction , PC or program counter stores the address of current instruction , and ALU executes current instruction. The interconnection of these simple components to form a basic datapath is illustrated in Figure 4.
Note that the register file is written to by the output of the ALU. As in Section 4. Schematic high-level diagram of MIPS datapath from an implementational perspective, adapted from [Maf01].
Implementation of the datapath for I- and J-format instructions requires two more components - a data memory and a sign extender , illustrated in Figure 4. The data memory stores ALU results and operands, including instructions, and has two enabling inputs MemWrite and MemRead that cannot both be active have a logical high value at the same time.
The data memory accepts an address and either accepts data WriteData port if MemWrite is enabled or outputs data ReadData port if MemRead is enabled , at the indicated address. The sign extender adds 16 leading digits to a bit word with most significant bit b , to product a bit word. In particular, the additional 16 digits have the same value as b , thus implementing sign extension in twos complement representation.
Implementation of the datapath for R-format instructions is fairly straightforward - the register file and the ALU are all that is required. Schematic diagram R-format instruction datapath, adapted from [Maf01]. In order to compute the memory address, the MIPS ISA specification says that we have to sign-extend the bit offset to a bit signed value. This is done using the sign extender shown in Figure 4. Memory Address Calculation decodes the base address and offset, combining them to produce the actual memory address.
This step uses the sign extender and ALU. Note that the execute step also includes writing of data back to the register file, which is not shown in the figure, for simplicity [MK98]. The sign-extended offset and the base address are combined by the ALU to yield the memory address, which is input to the Address port of the data memory. The MemRead signal is then activated, and the output data obtained from the ReadData port of the data memory is then written back to the Register File using its WriteData port, with RegWrite asserted.
If equal, the branch is taken. Otherwise, the branch is not taken. Thus, to jump to the target address, the lower 26 bits of the PC are replaced with the lower 26 bits of the instruction shifted left 2 bits. The branch instruction datapath is illustrated in Figure 4. Calculate Branch Target - Concurrent with ALU 1's evaluation of the branch condition, ALU 2 calculates the branch target address, to be ready for the branch if it is taken. This completes the decode step of the fetch-decode-execute cycle.
This effectively changes the PC to the branch target address, and completes the execute step of the fetch-decode-execute cycle. Schematic diagram of the Branch instruction datapath. The branch datapath takes operand 1 the offset from the instruction input to the register file, then sign-extends the offset.
The sign-extended offset and the program counter incremented by 4 bytes to reference the next instruction after the branch instruction are combined by ALU 1 to yield the branch target address. The operands for the branch condition to evaluate are concurrently obtained from the register file via the ReadData ports, and are input to ALU 2, which outputs a one or zero value to the branch control logic.
MIPS has the special feature of a delayed branch , that is, instruction I b which follows the branch is always fetched, decoded, and prepared for execution. If the branch condition is false, a normal branch occurs. If the branch condition is true, then I b is executed. One wonders why this extra work is performed - the answer is that delayed branch improves the efficiency of pipeline execution, as we shall see in Section 5.
Also, the use of branch-not-taken where I b is executed is sometimes the common case. Single-Cycle and Multicycle Datapaths Reading Assignments and Exercises A single-cycle datapath executes in one cycle all instructions that the datapath is designed to implement.
In this section, we first examine the design discipline for implementing such a datapath using the hardware components and instruction-specific datapaths developed in Section 4. Then, we discover how the performance of a single-cycle datapath can be improved using a multi-cycle implementation.
Single Datapaths Let us begin by constructing a datapath with control structures taken from the results of Section 4. The simplest way to connect the datapath components developed in Section 4. As a result, no datapath component can be used more than once per cycle, which implies duplication of components. To make this type of design more efficient without sacrificing speed, we can share a datapath component by allowing the component to have multiple inputs and outputs selected by a multiplexer.
The key to efficient single-cycle datapath design is to find commonalities among instruction types. However, the following differences can also be observed: The second ALU input is a register R-format instruction or a signed-extended lower 16 bits of the instruction e. These two datapath designs can be combined to include separate instruction and data memory, as shown in Figure 4. Adding the branch datapath to the datapath illustrated in Figure 4.
The branch instruction uses the main ALU to compare its operands and the adder computes the branch target address.
ALU Control. Given the simple datapath shown in Figure 4. Control accepts inputs called control signals and generates a a write signal for each state element, b the control signals for each multiplexer, and c the ALU control signal.
The ALU has three control signals, as shown in Table 4.
Arithmetic and Logical Unit ALU
Reading Assignments and Exercises This section is organized as follows: 4. The Central Processor - Control and Dataflow 4. Datapath Design and Implementation 4. Single-Cycle and Multicycle Datapaths 4. Controller Finite State Machines 4.
Arithmetic Logic Unit is the part of a computer that performs arithmetic operations on binary numbers. The inputs to an ALU are the data where we have to perform operations. They are called operands. They perform the necessary operation and the result is the output of the operation we have performed. Thus, the ALU consists of input or output or even both.
Show all documents These two operations are depends upon the number of selection lines to select a particularoperation in the unit. Mainly ALU contains two inputs which are control by the select line for the multi- operation. ALU defines for the two most important units and they are arithmetic and logic units. In this paper, the arithmetic unit defines for the bit adder, bit subtractor and bit comparator where in the logic units we define all the gates of bit. Arithmetic Unit. We describe the design of 1-bit Arithmetic Logic Unit based on combinational circuits which reduces the required hard-ware complexity and allows for reasonable simulation times.
Control other Logic. Unit. - Signals. Circuits. Flags. -. -. Figure 1: Structure & a fixed point Arithmetic logic unit. The organisation have three onc word registers.
Computer - CPU(Central Processing Unit)
It fetches internal instructions of the programs from the main memory to the processor instruction register, and based on this register contents, the control unit generates a control signal that supervises the execution of these instructions. A control unit works by receiving input information to which it converts into control signals, which are then sent to the central processor. The functions that a control unit performs are dependent on the type of CPU because the architecture of CPU varies from manufacturer to manufacturer. Examples of devices that require a CU are:. Types of Control Unit — There are two types of control units: Hardwired control unit and Microprogrammable control unit.
The basis of comparison include: Description, dependency, function and design. It performs all processes related to arithmetic and logic operations that need to be done on instruction words. In some processors, the arithmetic logical unit is divided into two units, an arithmetic unit AU and a logic unit LU.
5 Difference Between Arithmetic Logical Unit (ALU) And Control Unit (CU)
An error-correction method is proposed for computer arithmetic logic units, in which memory duplication is executed and an algebraic linear code with minimal information redundancy is used for control. Rules for the use of coded information have been formulated for error detection during execution of arithmetic and logical operations. A procedure is proposed for the formulation of the duplication channel of arithmetic logic units due to the use of equipment intended for coding of information and the functional redundancy of the arithmetic logic units of the processor.
The main function of the control unit is to fetch and execute instructions from the memory of a computer. It is included as a part of Von Neumann architecture developed by John Neumann. It is responsible for providing the timing signals, and control signals and directs the execution of a program by the CPU.
for arithmetic operations (the arithmetic unit, AU) and for logic operations (the logic unit, LU). I1 contains an integer AU and a floating-point AU. A complete discussion of an rithms, and logic circuits that control the sequence of inter-register.
ALU full form is Arithmetic Logic Unit , takes the data from Memory registers ; ALU contains the logical circuit to perform mathematical operations like subtraction, addition, multiplication, division, logical operations and logical shifts on the values held in the processors registers or its accumulator. It is the size of the word that the ALU can handle which, more than any other measure, determines the word-size of a processor: that is, a bit processor is one with a bit ALU. After processing the instructions the result will store in Accumulator. Control unit generates control signals to ALU to perform specific operations. The accumulator is used as by default register for storing data. It is bit register.
Show all documents The maximum drain current produces by dual gate mode is much higher than single gate mode. All the results are carried out using H-spice simulation tool. The simulation of ALU is carried at 32nm technology. The figure of merit measured for ALU are power and delay. Different kinds of computers have different ALUs. But all of the ALUs contain arithmetic unit and logic unit , which are the basic structures.
In computing , an arithmetic logic unit ALU is a combinational digital circuit that performs arithmetic and bitwise operations on integer binary numbers. It 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. The inputs to an ALU are the data to be operated on, called operands , 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 status registers. An 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.
The purpose of the CPU is to process data. The CPU is where processes such as calculating, sorting and searching take place. Whatever is done on our computers, such as checking emails, playing games and doing homework, the CPU has processed the data we use. The CPU is made up of three main components, the control unit , the immediate access store and the arithmetic and logic unit. The control unit controls the flow of data within the system.
The term microprocessor typically refers to the central processing unit CPU of a microcomputer , containing the arithmetic logic unit ALU and the control units. It is typically implemented on a single LSI chip. This separates the "brains" of the operation from the other units of the computer.
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