Control Unit
The control unit is a component of a computer's central processing unit (CPU) that manages and coordinates the execution of instructions. It fetches instructions from memory, decodes them, and controls the flow of data within the CPU. The control unit plays a crucial role in ensuring that instructions are executed in the correct sequence and at the right time.
3 Key excerpts on "Control Unit"
eBook - ePub- David Johnson(Author)
- 2020(Publication Date)
- CRC Press(Publisher)
...4 The Central Processing Unit Although referred to as the brain of the system, the Central Processing Unit in a normal installation is the unsung hero, buried in a control cabinet, all but forgotten. 4.1 BASIC FUNCTIONALITY In a programmable controller system, the central processing unit (CPU) provides both the heart and the brain required for successful and timely control execution. It rapidly and efficiently scans all of the system inputs, examines and solves the application logic, and updates all of the system outputs. In addition, it also gives itself a checkup each scan to ensure that its structure is still intact. In this chapter we will examine the central processing unit as it relates to the entire system. Included will be the various functional blocks in the CPU, typical scan techniques, I/O interface and memory uses, power supplies, and system diagnostics. 4.2 TYPICAL FUNCTION BLOCK INTERACTIONS In practice, the central processing unit can vary in its architecture, but consists of the basic building block structure illustrated in Figure 4.1. The processor section consists of one or more microprocessors and their associated circuitry. While it is true that some of the older generation programmable controllers were designed without the luxury of using microprocessors, most modern systems use either a single microprocessor such as the 8086 or Z-80, or multiple microprocessors such as the AMD2903, used in a bit slice architecture. This multi-tasking approach is used in the multiple microprocessor system to break the control system tasks into many small components which can be executed in parallel. The result of this approach is to achieve execution speeds that are orders of magnitude faster than their single-tasking counterparts...
eBook - ePubElectronics Explained
The New Systems Approach to Learning Electronics
- Louis E. Frenzel(Author)
- 2010(Publication Date)
- Newnes(Publisher)
...This is called the fetch-execute cycle, which is repeated on each instruction until the program runs to completion. The execution of each instruction may call for accessing one or more data words in the memory or storing a data word in memory. The ALU is the section of the computer that carries out many of the functions that are specified by the instructions. In other words, the ALU actually processes the data. Specifically, the ALU carries out two main types of processing: arithmetic operations (such as addition, subtraction, multiplication, and division) or logic operations (such as AND, OR, complement, or exclusive OR). For example, if an add instruction is stored in memory, the control section will fetch it, interpret it, and send signals to the ALU that cause two numbers to be added. The ALU also performs data movement operations. It can move data or instruction words from one place to another inside the CPU or it can carry out memory read/write or input/output operations. These are called load and store instructions. A key part of the CPU associated with the ALU is the registers. Most ALUs have two or more registers. High-powered CPUs may have a group of 16 or more registers, called general-purpose registers (GPRs). The registers are used to temporarily store the data being processed by the ALU and the results of the computations. Other registers in the CPU store a number called an address where the data or instructions are stored, store the instruction being executed, or act as a stop-off place for data into or out of the CPU. The control section, ALU, and the registers in all micros are very closely related. They operate together and are always considered as a single unit. As indicated earlier, the combination of the control and the ALU sections is called the CPU (see Figure 6.4). In addition, microprocessors are single-chip CPUs. Besides being called CPUs, microprocessors are sometimes called MPUs or microprocessing units...
- Mohamed Rafiquzzaman(Author)
- 2021(Publication Date)
- CRC Press(Publisher)
...The ALU usually performs operations such as binary addition and subtraction. The 32-bit microprocessors include multiple ALUs for parallel operations and thus achieve fast speed. The Control Unit of the microprocessor performs instruction interpreting and sequencing. In the fetch phase, the Control Unit reads instructions from memory using the PC as a pointer. It then recognizes the instruction type, gets the necessary operands, and routes them to the appropriate functional units of the execution unit. Necessary signals are issued to the execution unit to perform the desired operations, and the results are routed to the specified destination. In the sequencing phase, the Control Unit determines the address of the next instruction to be executed and loads it into the PC. The Control Unit is typically designed using one of three techniques: • Hardwired control • Microprogramming • Nanoprogramming The hardwired Control Unit is designed by physically connecting typical components such as gates and flip-flops. Typical 32-bit RISC microprocessors such as the Intel 80960 and Motorola 88100 are designed using hardwired control. The microprogrammed Control Unit includes a control ROM for translating the instructions. Intel 8086 is a microprogrammed microprocessor. Nanoprogramming includes two ROMs inside the Control Unit. The first ROM (microROM) stores all the addresses of the second ROM (nanoROM). If the microinstructions (which is the case with the 68000/68020/68030/68040) repeat many times in a microprogram, use of two-level ROMs provides tremendous memory savings...
