Computer Bus PDF

IT1910 Computer Bus It is a communication pathway that connects two (2) or more devices or modules used for transferring data. It consists of a set of conductors. Examples of these conductors are ribbon cables, external cabling, copper tracks on a printed circuit board, microscopic aluminum trails...

IT1910 Computer Bus It is a communication pathway that connects two (2) or more devices or modules used for transferring data. It consists of a set of conductors. Examples of these conductors are ribbon cables, external cabling, copper tracks on a printed circuit board, microscopic aluminum trails on the surface of a silicon chip, and other many forms. Each devices connected to the computer bus, in a form of trailings or wires, transmits a bit of data (1 or 0). Thus, the collection of wires is capable of transferring a byte or a word at a time as a function of its width. Architecture of a System Bus In reality, each bus consists of 50 to 100 distinct physical lines divided into three (3) subassemblies: Address bus (memory bus) – It is a unidirectional bus that transports memory addresses which the processor wants to access to read or write data. Data bus – It is a bidirectional bus that transfers instructions coming from or going to the processor. Control bus (command bus) – It is a bidirectional bus that transports orders and synchronization signals coming from the control unit and traveling to all other hardware components. It also transmits response signals from the hardware. Methods of Data Transmission There are two (2) kinds of data transmission methods that are frequently used in data communication: Serial – It is normally used for long-distance data transfer and in cases where the amount of data being sent is relatively small. It ensures that the data integrity is maintained as it transmits the data bits in a specific order, one after another. Data bits are sent one by one in a medium. Parallel – When data is sent using parallel data transmission, multiple data bits are transmitted over multiple channels at the same time. This implies that data can be sent faster than using serial transmission methods. Serial Bus versus Parallel Bus The comparison of the two (2) buses implies similarities and differences for a specific purpose of data transmission. These buses are used in different applications and functions (see Table 1). PARALLEL BUS SERIAL BUS Transmits several streams of data simultaneously Can transmit fewer data in faster clock cycle to along multiple channels achieve a higher data rate Widely used within integrated circuits Requires fewer interconnecting cables (e.g., Half-duplex – the data is either sent or received wires and fibers) and occupies less space Used for a short distance Full-duplex – the sender can send and receive data simultaneously Used for long-distance communication Table 1. Comparison of parallel bus and serial bus Bus Communication Protocols A bus transfers electrical signals from one place to another. Data travels between the CPU and memory along the data bus. The location (address) of that data is carried along the address bus. There are two (2) types of bus protocols: Synchronous – Data bits are transmitted as a continuous stream in time with a master clock. The data transmitter and receiver both operate using a synchronized clock frequency; therefore, start bits, stop 05 Handout 1 *Property of STI  [email protected] Page 1 of 4  IT1910 bits, and gaps are not used. This implies that data moves faster and timing errors are less frequent because the transmitter and receiver time is synced. However, data accuracy is highly dependent on timing being synced correctly between devices. Asynchronous – Data bits can be sent at any point in time. Stop bits and start bits are used between data bytes to synchronize the transmitter and receiver and to ensure that the data is transmitted correctly. The time between sending and receiving data bits is not constant; thus, gaps are used to provide time between transmissions. Bus Arbitration More than one (1) module may need control of the bus (e.g., CPU and DMA controller). The I/O module may need to read or write directly to memory, without sending the data to the processor. The process by which multiple requests are recognized and priority is given to one of them is called arbitration. Centralized Arbitration o In here, an arbitration circuit receives requests from the contending bus masters and then decides which of them is to be given control of the bus. o A single hardware device, known as a bus controller or arbiter, is responsible for allocating time to bus. o The device may be part of the CPU or a separate module such as daisy-chaining. Distributed Arbitration o There is no central controller. Each module may claim the bus. o All devices monitor all the request lines. o In a system with distributed arbitration, each of the masters takes part in the arbitration process. o The system lacks a specific arbiter—each master monitors the other masters and decides whether to continue competing for the bus or give up and wait until later. Characteristics of a Computer Bus Listed below are the common characteristics that a computer bus must have. Data Sharing – All types of buses found in computer transfer data between computer peripherals connected to it. Addressing – A bus has address lines that match those of the processor. This allows data to be sent to or from specific memory locations. Power – A bus supplies power to various peripherals connected to it. Timing – A bus provides a system clock signal to synchronize the peripherals attached to it with the rest of the system. Chipset A chipset is a component that routes data between a computer’s buses. This enables all of the components that make up the computer to communicate with each other. Northbridge (memory controller) is in charge of controlling the transfer of data between the processor and the random access memory (RAM), which is why it is located physically near the processor. o Internal Bus (Front-Side Bus or FSB) – This allows the processor to communicate with the system’s central memory or the RAM. Southbridge (input/output controller or expansion controller) handles communications between peripheral devices. It is also called the ICH (I/O Controller Hub). 05 Handout 1 *Property of STI  [email protected] Page 2 of 4  IT1910 o Expansion Bus (Input/Output Bus) – This allows various motherboard components (i.e., USB or serial) to communicate with one another. Computer Bus Technologies Here are some of the common expansion bus types that were used in computers: Previously Used Technology Industry Standard Architecture (ISA) – IBM introduced this bus for IBM PC using an 8088 microprocessor. This has an 8-bit data bus and 20 address lines at a clock speed of 8 MHz. Video Electronics Standards Association (VESA) – This bus is a standard interface between a computer and its expansion. As applications became more graphically intensive, the VESA bus was introduced to maximize throughput of video graphics memory. This also provides fast data flow between stations and can transfer up to 132 Mbps. Accelerated Graphics Port (AGP) – This is connected to the CPU. This operates at the speed of the processor bus and implies that video information is sent quickly to the card for processing. The data transfer rate ranges from 264 Mbps to 528Mbps and 800 Mbps up to 1.5 Gbps. The AGP connector is identified by its brown color. Peripheral Component Interconnect (PCI) – Intel Corporation developed this bus. The PCI bus technology includes a 32- or 64-bit bus that runs at 33/66 MHz clock speed. It offers many advantages for connections to hubs, routers, and network interface cards (NIC). In particular, PCI provides more bandwidth up to 1 Gigabit per second as needed by these hardware components. Currently Used Technology Small Computer Systems Interface (SCSI) – It is a set of ANSI (American National Standards Institute) standard electronic interfaces that allows PCs to communicate faster with peripheral hardware (e. g., disk drives, tape drives, CD-ROM drives, printers, and scanners). It is more flexible than previous parallel data transfer interfaces. Personal Computer Memory Card Industry Association (PCMCIA) – This was founded to give a standard bus for laptop computers. A PCMCIA card has a 68-pin connector that connects into a slot in the PC. These cards are plug-and-play devices that are often hot-swappable in most of the operating systems. Peripheral Component Interconnect Express (PCIe) – It is an interface standard for connecting high- speed components. PCIe slots come in different physical configurations: x1, x4, x8, x16, x32. The number after the “x” implies the number of lanes (how data travels to and from the PCIe card) that a PCIe slot has. Universal Serial Bus (USB) – It connects peripheral devices such as digital cameras, mice, keyboards, printers, scanners, media devices, external hard drives, and flash drives. It is intended to enhance plug- and-play and to allow hot-swapping. Plug-and-play enables the operating system to configure and discover a peripheral device spontaneously without having to restart the computer. Additionally, hot-swapping allows removal and replacement of a new peripheral without having to reboot. Because of its wide variety of uses, including support for electrical power, the USB has replaced a wide range of interfaces like the parallel and serial ports. 05 Handout 1 *Property of STI  [email protected] Page 3 of 4  IT1910 References: Berekovic, M., Buchty, R., Hamann, H., Koch, D., & Pionteck, T. (2018). Architecture of computing systems – ARCS 2018 proceedings. Switzerland: Springer Nature. Computer Bus - What Is It? (n.d.). In CCM. Retrieved from https://ccm.net/contents/375-computer-bus-what-is-it on June 27, 2019 David Keizer. (2016, June 6). RISC vs CISC [Video file]. Retrieved from https://www.youtube.com/watch?v=_EKgwOAAWZA on May 21, 2019 Edgington, A. (2017, July 17). The Ultimate Guide to USB Cables [Image]. Retrieved 2019, June 27 from https://www.conwire.com/ultimate-guide-usb-cables/ Education 4u. (2017, December 11). daisychain arbitaration | COA | [Video file]. Retrieved 2019, June 27 from https://www.youtube.com/watch?v=0GUW00xU9E8 Elahi, A. (2018). 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