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CHAPTER 8

CHAPTER 8. EXPANSION BUSES, CABLES AND CONNECTORS. Chapter Overview. Understanding Expansion Buses Configuring Expansion Cards Cables and Connectors. Understanding Expansion Buses. Expansion Buses connect devices to the M/B using the M/Bs data bus.

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CHAPTER 8

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  1. CHAPTER 8 EXPANSION BUSES, CABLES AND CONNECTORS

  2. Chapter Overview • Understanding Expansion Buses • Configuring Expansion Cards • Cables and Connectors

  3. Understanding Expansion Buses • Expansion Buses connect devices to the M/B using the M/Bs data bus. • Early computers moved data between devices and the processor at about the same rate as the processor. As processor speed increased, the movement of data through the bus became a holdup. overview

  4. Development of the Expansion Bus • Every device in the computer is connected to the external data bus. • The function of an expansion slot is to provide configuration flexibility when devices are added to a computer. • Whether a device is soldered to the M/B or connected through an expansion slot, all ICs are regulated by a quartz crystal. • A specific CPU is described by it's manufacturer, model, and speed in megahertz (MHz). A computer's system board has a quartz crystal on it that emits a constant signal or beat. Each beat is called a clock cycle and is measured in MHz, or millions of cycles per second. • The crystal sets the timing for the system. • Most CPUs divide the crystal speed by two ( if the CPU has a 33-MHz speed, a 66-MHz crystal is required.

  5. Development of the Expansion Bus Cont. - External data bus divided into two parts: • System bus is the series of connections between the CPU and the system memory, this support the CPU , RAM and other M/B components and runs at speeds that support the CPU. . • Expansion bus connects any add-on devices to the computer system. Runs at steady state , based on the specific bus design. • Upgrading a CPU requires changing only the timing of the system bus. • Expansion buses include the following types: • Industry Standard Architecture (ISA), Micro Channel Architecture (MCA), Extended Industry Standard Architecture (EISA) • VESA local bus (VLB), Peripheral Component Interconnect (PCI), Accelerated Graphics Port (AGP) • Institute of Electrical and Electronics Engineers (IEEE) 1394 (FireWire), universal serial bus (USB)

  6. Industry Standard Architecture(ISA) • The First-generation IBM XT ( with the 8088 processor), had an 8-bit external data bus and ran at a speed of 4.77MHz..these machines were sold with an 8-bit expansion bus that ran at 8.33 MHz • Problems with ISA design • Lack of speed • Compatibility problems Note: 8-bit slot is called the XT, and the 16 –bit slot is called the AT.

  7. ISA bus pin configuration Soldier Side Components Side

  8. MicroChannel Architecture (MCA) • In 1986 the market came to be dominated by the new 386 machines with their 32-bit architecture. • IBM designers produced a new version of the PC, the PS/2 ( personal system/2) and created a proprietary expansion bus called MCA as part of the design , running at 10-MHz, it offered more performance and provided a 32-bit data path. • A feature of MCA was its ability to “ self-configure” devices. MCA device always came with a configuration disk, so the IRQ, I/O addresses and dirct memory access DMA were configured automatically.

  9. Extended ISA ( EISA) • EISA is an improved variation of the ISA slot.EISA is faster and cheaper than MCA.

  10. VESA Local Bus (VLB) The hardware industry developed the VESA local bus (VLB) to meet the need for a faster expansion interface. VESA, the video Electronics Standards Association, was the driving force behind the new bus technology) Read page 152

  11. Two performance-boosting features • Burst mode: VLB devices gain complete control of the external data bus for up to 4 bus cycles, passing up to 128-bits of data in a single burst. • Bus mastering: allows the VLB controller to arbitrate data transfers between the external data bus and up to three VLB devices without assistance from the CPU.

  12. Peripheral Component Interconnect (PCI) • Overcomes limitations of ISA, EISA, MCA, and VLB, and it offers the performance needed for today’s fast systems. • The original PCI design operates at 33 MHz . • Full arbitration of PCI local bus. This allows support of more than three slots. • The PCI bus has its own set of four interrupts. • Are also differences in PCI versions

  13. PCICont. • The early PCI M/Bs often have jumpers and BIOS settings that must be set to enable proper PCI operation. • PCI bus can deliver data transfers up to 132 MB per second. • PCI is not used only by PCs . Macintosh and other non-PC style computers include PCI.

  14. Accelerated Graphics Port (AGP) Intel led the way and developed the AGP. The AGP removes all the display data traffic from the PCI bus and gives that traffic its own 525-MB-per-second pipe into the system ship sets and from there , straight to CPU. It provides a direct path to the system memory for handling graphics. This procedure is referred to as direct memory execute (DIME). AGP connectors are found only on Pentium II-based and later computers or on similar CPUs from non-Intel vendors.

  15. IEEE 1394 (FireWire) • FireWire is an Apple brand name for the IEEE 1394 interface. It is also known as i.Link (Sony’s name) or IEEE 1394 (although the 1394 standard also defines a backplane interface). It is a personal computer (and digital audio/digital video) serial businterface standard, offering high-speed communications. FireWire has replaced Parallel SCSI in many applications, due to lower implementation costs and a simplified, more adaptable cabling system • Interface originally developed by Apple • High-speed serial interface with data • Advantages: hot swap, inexpensive connectors, simple cable design • Direct path to system memory • Not presently a widely used standard

  16. Universal Serial Bus (USB) • Connects peripherals outside the computer • Supports speeds of 1.5 Mbps for asynchronous transfer rate for devices such as a mouse or keyboard. • 12 Mbps for isochronous transfer rate for high bandwidth devices such as modem, speakers, scanners. • USB devices can be attached with the computer running. • Offers the following advantages: • Hot swap ( the ability to add and remove components while the machine is running) • Recognition of new device by operating system (OS) • Ease of adding new devices

  17. Pin Name Description 1 VCC +5 VDC 2 D- Data - 3 D+ Data + 4 GND Ground Mini USB Connector

  18. Configuring Expansion CardsHow the computer keeps track of each device and controls the flow of data. • The bus system establishes a connection between the CPU and expansion devices and provide a path for the flow of data. • Computer needs a way to track and control which device is sending data and which device is receiving . • The First step to establishing organized communication is to assign a unique I/O address to each device. • I/O addresses are patterns of 1s and 0s transmitted Across the address bus by the CPU.

  19. Configuring Expansion Cards Cont. • The CPU must identify the device before any data is placed on the bus. • CPU uses two bus wires- the Input/Output read (IOR) and Input/ Output Write ( IOW) to notify the devices that the address bus is not being used to specify an address in memory. • All devices must have an I/O address, and no two devices can have overlapping ranges.

  20. The Most Common I/O Addresses

  21. Setting and Managing I/O Addresses • Non–Plug and Play I/O addresses are set with jumpers, dual inline package (DIP) switches, and software drivers. • Plug and Play devices are self-configuring and can conflict with older non–Plug and Play cards. • Devices with overlapping I/O addresses will not respond to commands, sound card will start to play but will stop, a modem will dial but not connect. • On plug and play systems, PCI cards are self configuring. Note : Watch the jumpers video

  22. Interrupt Request (IRQ) • An IRQ or Interrupt Request Line allows a hardware device inside of the computer a direct line to the microprocessor and tells the microprocessor to stop what it is doing when the device needs attention. The interrupt request signals run along the IRQ lines to an INTERRUPT CONTROLLER that assigns priorities to incoming IRQs and delivers them to the CPU. The interrupt controller is hardware found on the motherboard in a larger chip as part of a chipset. • The 8259 acts as a multiplexer, combining multiple interrupt input sources into a single interrupt output to interrupt a single device.

  23. Steps of Interrupt Process. • The device applies voltage to the 8259 chip through its IRQ wire. • The 8259 chip informs the CPU, by means of the INT wire , that an interrupt is pending. • The CPU uses a wire called an INTA ( interrupt acknowledge) to signal the 8259 chip to send a pattern of 1s and 0s on the external data bus, this information express to the CPU which device is interrupting. A timer is a specialized type of clock. A timer can be used to control the sequence of an event or process. Timers can be mechanical, electromechanical, digital, or even software, since most computers include digital timers of one kind or another. For x=0; X=0 to 10 x=x+1

  24. Cascading the 8259 Chip • The 8088 computers used only one 8259 chip. Which limited to use only eight available IRQs. • Two 8259 chips were used to add 8 more available IRQs.

  25. Setting IRQs • Set IRQs during installation. • Use hardware, software, or a combination of both to set IRQs. • Document all IRQ settings.

  26. Direct Memory Access (DMA) • Direct memory access (DMA) is a feature of modern computers, that allows certain hardware subsystems within the computer to access system memory for reading and/or writing without help of the central processing unit. Many hardware systems use DMA including disk drive controllers, graphics cards, network cards, and sound cards. Computers that have DMA channels can transfer data to and from devices with much less CPU overhead than computers without a DMA channel. • Direct Memory Access (DMA) is another I/O interfacing technique. DMA controller transfers data from a drive or other peripheral device directly to the computer's memory without CPU intervention. A DMA controller is designed to service one or more Input/Output devices. Each service interface is called a channel. It takes the load of the processor and results in faster overall data transfer.

  27. DMA Cont. The standard computer (PC) has two DMA controllers. The first controls channels 0,1,2,3 and the second channels 4,5,6,7. Thus we have 8 channels altogether. However, channel 4 is lost since it is used by the Direct Memory Access controller. The direct memory access (DMA) chip (8237) offloads work from the CPU. Each 8237 chip supports four devices. Two DMA chips are cascaded to provide eight DMA channels.

  28. Setting and Managing DMA Channels ECP = Extended Capabilities Port SCSI = Small Computer System Interface

  29. Setting up ECP (Extended Capabilities Port) with your printer. An ECP, or Extended Capabilities Port, is an enhanced version of a regular parallel port. Configuring your system and your printer to work with ECP can greatly improve your printing speed and performance. Locate your computer or add-in card’s manual. You will need to find out the DMA and IRQ settings for each ECP port you want to use. You will need this information to setup ECP properly. To do this: Click the start button. Select settings Click control panel Once you are there, double-click the System icon. Click the Device Manager tab. Click "Ports (COM & LPT)." Select your ECP device. (it will only appear if your system is capable). Click Properties. Click the Resources tab. Under Settings Based on Field, select Basic Configuration 2. Under the Resource Settings list, click Interrupt Request. Click Change Settings. In the Edit Interrupt Request dialog box, type in the IRQ you should have found from the manual or another place. Click OK. Under Resource properties, click on Direct Memory Access. From the Edit Direct Memory Access dialog box, type in the DMA you should have found from the manual or another place. Click OK. Shut off your computer and wait 3 seconds. Now reboot your computer and the new settings will be in place. My computer properties hardware  device manager view

  30. COM and Ports • IBM created preset combinations of IRQs and I/O addresses for serial and parallel devices. • Port means a portal or two-ways access. • The preset combinations are called COM ports for serial devices and LPT ports for parallel devices.

  31. Serial and Parallel Ports A serial port is male in gender, and has either 9 pins or 25 pins. The shape of the port is slightly D-shaped. A serial computer port may be used for a mouse, external modem, scanner, or other linking software such as for a personal data assistant (PDA). A parallel port is female in gender, and has 25 pins. The shape of the port is slightly D-shaped. This is the same port as where your printer attaches. On most computers, there is only 1 port and it can be marked as LPT or with a printer symbol.

  32. COM Ports • COM1 and COM3 share IRQ4. • COM2 and COM4 share IRQ3. • COM3 uses I/O port 3E8–3EF and COM1 uses 3F8–3FF. • COM4 uses I/O port 2E8–2EF and COM2 uses 2F8–2FF.

  33. LPT Ports • You should use IRQ7 for LPT1 and IRQ5 for LPT2. • IRQ5 is typically used by sound cards. • Devices other than printers can use LPT ports. • The USB is taking over many of the parallel designs.

  34. Installing Expansion Cards • Read the documentation. • Document addresses and DMA and IRQ settings. • Keep settings unique, and document them.

  35. Parallel Printer Cables

  36. IEEE 1284 Printer Modes • It is important to configure the correct mode for each printer. • Each pin assignment corresponds to a specific function.

  37. Serial Port Cables

  38. Null Modem and SCSI Cables • Null modem cable: used to directly connect two computers • SCSI cable: used to connect a variety of internal and external devices

  39. Keyboard Cables

  40. Identifying Cables and Connectors • Communication • Printer • Monitor • Game port • Keyboard Check page 174

  41. Troubleshooting Cables • Always check the cable first. • Always check for loose connections. • Check for bent or broken pins. • Do not use force. • Ensure that you are using the correct cable. • Avoid “homemade” cables.

  42. Summary of Connectors • DB-9, DB-25: used for serial and parallel port communications, respectively • RJ-11, RJ-12: standard telephone connectors • RJ-45: network connector • PS/2 (mini-DIN): supports mouse, scanners, and some keyboards • Centronics: supports printers • USB: supports a variety of peripheral devices

  43. Chapter Summary • Expansion buses are standardized connections for installing devices. • Expansion buses have several architecture types. • All devices require unique I/O addresses, IRQs, and DMA channels. • IRQ conflicts cause most problems during installation of a new device. • COM ports are used for serial devices, and LPT ports are used for parallel devices. • It is important to identify cables and connectors. • Loose or poorly connected cables often cause computer problems.

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