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MICROCOMPUTER FOR CONTROL SYSTEMS
Microcomputer the Beginning While IBMwere blazing a trail, many other manufacturerswere close behind. The standards set by IBM attracted much interest from other manufacturers, notable among whom were Compaq and Olivetti. These companies were not merely content to produce machines with an identical specification but went on to make further significant improvements. Other manufacturers were happy to simply ‘clone’ the PC; indeed, one could be excused for thinking that the highest
Setting up a PC requires access to both hardware and software
Chapter This chapter sets out to introduce the PC and provide an insight into the architecture, construction, and operation of a ‘generic PC’. It should, perhaps, be stated that the term ‘PC’ now applies to such a wide range of equipment that it is difficult to pin down the essential ingredients of such a machine. Other factors, such as available memory size, disk capacity, and display technology remain secondary.
Elements of Microcomputer Systems The principal elements within a microcomputer system consist of a central processing unit (CPU), read/write memory (RAM), read-only memory (ROM), together with one (or more) input/output (I/O) devices.
Elements of a microcomputer system
Bus Systems The elements within the microcomputer system shown in Figure (CPU, ROM, RAM, and I/O) are connected together by three distinct bus systems: 1 The address bus along which address information is passed. 2 The data bus along which data is passed. 3 The control bus along which control signals are passed.
Data Representation The information present on the bus lines is digital and is represented by the two binary logic states: logic 1 (high) and logic 0 (low) Data is passed via the data bus line in parallel groups of either 8, 16, 32, or 64 bits. An 8-bit group of data is commonly known as a byte whereas a 16-bit group is usually referred to as a word.
Data representation in a microcomputer system
Relationship between data bus size and largest data value Relationship between address bus lines and linear addressable memory
Bus Expansion The system shown in Figure can be expanded by making the three bus systems accessible to a number of expansion modules.These modules (which invariably take the form of plug-in printed circuit cards) provide additional functionality associated with input/output (I/O), graphics, or disk control. Expansion cards are often referred to as ‘option cards’ or ‘adapter cards’, and they provide a means of extending a basic microcomputer system for a particular application.
Microcomputer system with bus expansion capability
ISA expansion card which provides two serial and two parallel ports
Microprocessor Operation The majority of operations performed by a microprocessor involve the movement of data. Indeed, the program code (a set of instructions stored in ROM or RAM) must itself be fetched from memory prior to execution.
Data Transfer and Control The transfer of data to and from I/O devices (such as hard drives) can be arranged in several ways. The simplest method (known as programmed I/O, involves moving all data through the CPU. Interrupt request (IRQ) Direct memory access (DMA) Additional DMA request (DRQ) and DMA acknowledge (DACK) signals are necessary so that the CPU is made aware that other devices require access to the bus.
Data Transfer and Control (2) Interrupt request (IRQ) is a signal that is sent to the CPU when a peripheral device requires attention (this topic is described in greater detail later in this chapter). The advantage of this method is that CPU intervention is only required when data is actually ready to be transferred or is ready to be accepted (the CPU can thus be left to perform more useful tasks until data transfer is necessary).
Data Transfer and Control (3) Direct memory access (DMA), provides a means of transferring data between I/O and memory devices without the need for direct CPU intervention. Direct memory access provides a means of achieving the highest possible data transfer rates, and it is instrumental in minimizing the time taken to transfer data to and from the hard disk or another mass storage device.
Parallel versus Serial I/O Most microcomputer systems (including the PC) have provision for both parallel (e.g. a parallel printer) and serial (e.g. an RS-232 port) I/O. Parallel I/O involves transferring data one (or more) bytes at a time between the microcomputer and peripheral along multiple wires; usually eight plus a common ground connection). Serial I/O, on the other hand, involves transferring 1-bit after another along a pair of lines (one of which is usually a ground connection).
Data conversion: serial-to-parallel
Data conversion: parallel-to-serial
The Processor The processor, or central processing unit (CPU), is crucial in determining the performance of a PC and processors have been consistently upgraded since the first PC arrived on the scene in In modern PCs, the overall device count has been significantly reduced by integrating several of the functions associated with the original PC chipset within one or two VLSI devices or within the CPU itself.
Development of the ’x86 Intel processor family
Chipset One of the functions of the chipset is to act as a bridge between the various bus systems, managing the data flow and ensuring the efficient transfer of data The front side bus (FSB) allows data to be transferred at high speed between the processor, memory controller, and graphics controller whilst the back side bus (BSB) allows the processor to be fed with an instruction stream from the level 2 cache memory
Architecture of a Modern PC
North Bridge and South Bridge Architecture This architecture uses a North Bridge and South Bridge (both separate chips within the chipset). The North Bridge provides the processor with an interface to the memory bus, advanced graphics port bus (AGP) and the PCI expansion bus. The South
North Bridge and South Bridge Architecture (2)
Layout for a Modern PC (motherboard)
Layout of Embedded PC Controller
Memory Speed The speed of memory is one of the most important factors in defining the performance of a system. Furthermore, memory speed forms (or the speed of memory components) forms an essential part of specification of every PC. Memory fitted to the PC must comply with this specification and failure to observe this prerequisite may cause a wide variety of problems including lock-ups, re-booting, and failure to boot.
Some of the most significant milestones in the development of memory devices are listed below:
Output of the BIOS data program
Disk Drives Disk drives provide low-cost high-capacity storage for data and programs. Standard floppy disk drives operate at 300 rpm and use an 80-track format with 135 tracks per inch. The standard data transfer rate is around 250 KB/s while the formatted storage capacity is 1.44MB. Modern Integrated Drive Electronics (IDE) hard drives are designed to interface very easily with the PC bus by means of one, or more, 40-way IDC connectors on the motherboard. The 40-way bus extension is sometimes known as an AT attachment (ATA).
DIMM, ATA/IDE, and power connectors on modern motherboard
Disk Drives (2) The next generation of hard drives are set to use the newly introduced Serial ATA (SATA) interface which is now becoming widely available. Existing parallel ATA drives transfer data concurrently on multiple parallel wires within an 80-wire cable. In contrast, SATA drives transfer data at high speeds over a thin 7-wire cable. Serial ATA drives offer several advantages over IDE drives, not the least of which is speed. The maximum data transfer rate (or burst rate) for most parallel drives is between 100 and 133 MB/s whilst drives using the first generation of the SATA interface can often reach 150 MBps. SATA drive speeds are expected to increase significantly over the next few years.
Having decided upon the platform for your application, whether it be a conventional PC, an industrial PC, or some form of embedded PC controller, there is a need to find an effective means of connecting your hardware via an appropriate interface. A large number of manufacturers have recognized this fact and have developed expansion cards specifically for control, data acquisition, and instrumentation applications.
PC expansion can be readily achieved by means of cards connected to the PC bus by any one or more of the following general methods: Connectors available on the system motherboard (e.g. ISA/EISA, PCI, or PCI-X); an external backplane bus or a stacking bus system (e.g. PC/104 and PC/104-Plus); a high-speed serial interface to the external hardware (e.g. USB); serial and/or parallel ports available on the motherboard.