Riyadh Philanthropic Society For Science Prince Sultan College For Woman

1. Riyadh Philanthropic Society For Science Prince Sultan College For Woman Dept. of Computer & Information Sciences CS 251 Introduction to Computer Organization & Assembly Language Lecture 9 (Computer System Organization) Input / Output

2. Outline • Study from Lecture notes • Logical Structure of a Simple Personal Computer • I/O-mapping • Direct Memory Access • Interrupt • Bus Arbiter & Cycle Stealing • Buses • A Typical Modern PC • Input / Output Devices Input / output

3. Introduction Input / output • Motherboard = large printed circuit board • The motherboard consists mainly of the following components: • The CPU chip. • Some slots. • Various support chips. • A bus along its length. • Sockets into which the edge connectors of I/O board can be inserted. • Sometimes there are two buses: • A high-speed bus for modern I/O boards. • A low-speed bus for older I/O boards.

4. Logical Structure of PCs Input / output • Each I/O device consists of two parts: • The device. (e.g. keyboard, monitor, etc.) • The controller, which controls the device and handle bus access for it.

5. Input / Output Mechanism • There are three different types of I/O that a typical computer system will use: • Port mapped I/O • Memory mapped I/O • Direct Memory Access • For each of these types, there are advantages and disadvantages Input / output

6. I/O Mechanism – Port mapped Input / output • CPU uses special instructions to access the I/O ports • This type is not provided by all CPUs • The Intel 80x86 Family processors • supports this type of I/O • Has In and OUT instructions to provide I/O mapped input/ output characteristics

7. I/O Mechanism – Memory Mapped Input / output • Peripheral devices are connected to the address and data line of the CPU exactly like the memory • CPU reads/writes the address of the peripheral device to transfer data to/from the device

8. I/O Mechanism – DMA Input / output • Direct Memory Access • Special Form of Memory mapped I/O • The I/O peripheral devices read/write data without going through the CPU • The CPU is not involved in the memory access

9. Interrupt Input / output • I/O devices must be able to initiate communication with the CPU. • An interrupt is a signal initiated by the I/O devices to tell the CPU that it requires some attention. • When the CPU is “interrupted”, it suspends running its current program and start running a special procedure, called an interrupt handler • The interrupt handler determines the appropriate course of action (e.g. Check for error, informs the OS that I/O is completed, etc.). • When the interrupt handler finishes, the CPU continues with the program that was suspended when the interrupt occurred.

10. Bus Arbiter & Cycle Stealing Input / output • The bus is not only used by the I/O controllers, but also by the CPU for fetching instructions and data. • A bus arbiter decides who takes the bus in case there is a collision • In general, the I/O devices are given preferences over the CPU • When no I/O is in progress, the CPU could have all the bus cycles to access memory • When some I/O device is also running, that device will request and be granted the bus when it needs it • This is what is called Cycle Stealing

11. Buses of information being communicated Input / output • Communication pathway between all components • Shared among all, thus broadcasts the information to all devices that are connected to it • Organize communication information into 3 forms • Address • Data • Control everything else

12. Bus Interconnection Scheme I/O memory Input / output

13. Data Bus Input / output • carries data • remember that there is no difference between “data” and “instruction” at this level • width is a key determinant of performance of bus. Can be 8, 16, 32, 64 bit.

14. Address Bus Input / output • Identify the source or destination of data • e.g. CPU needs to read an instruction (data) from a given location in memory • Bus width determines maximum memory capacity of system (Maximum Cells addressable)

15. 1 address 0 1 data 0 1 address data 0 Address & Data Groups Input / output • often bundle address and data signals separately and use different physical pathways • may multiplex using same physical pathway

16. Common Control Signals Input / output • reset – force all components to reset • clock(s) to synchronize communication. • destination indicator – usually memory or I/O device. • acknowledgment from component – info received from parts of computer • interrupts • Arbitration: Signal for Bus access by devices

17. Bus Protocols Input / output • signaling and sequencing to permit interactions between components of computer • Ex.. Memory Read • processor puts address value on bus, and “memory read” control indication • memory receives read signal, reads address, gets appropriate data, puts data on bus • processor waits, then reads data from bus • May be • Synchronous – protocol synchronized by a clock – organize protocol by clock “ticks”  Ti • Asynchronous – no clock is required to synchronize protocol.

18. Synchronous Memory Read T1 T2 T3 Assumption: Sensing of bus signals done during clock trailing edge clock mem read stable address addrs data stable data T1 initiate memory read (address, mem read signal) T2 time for memory to do internal work T3 data ready for reading from bus Input / output

19. Asynchronous Memory Write no shared clock pacing the protocol mem write command processor Memory sends signal that it has finished writing. Input / output

20. ISA, EISA & PCI Buses Input / output • One of the earliest bus architectures in the IBM PC was the ISA • (Industry Standard Architecture) bus. • This bus was too slow for market development • The situation led to other companies developing machines with multiple buses, one of which was the old ISA bus, or its backward- compatible successor, the EISA (Extended ISA) bus. • The most popular of these now is the PCI (Peripheral Component Interconnect) bus

21. Typical Modern PC Input / output

22. Typical Modern PC (Cont.) Input / output • A typical modern PC would typically contain: • Three or four empty PCI slots. • Three or four empty ISA slots. • To allow customers to plug in both • New PCI I/O cards, usually for fast devices. • Old ISA I/O cards, usually for slow devices.

23. Terminals Input / output • Computer terminals consist of two parts: • Keyboard. • Monitor. • In the mainframe world, these parts are often integrated into a single device and attached to the main computer by a serial line or over a telephone line • In the personal computer world, the keyboard and monitor are independent devices.

24. Keyboards Input / output • Keyboards rely on various methods to physically register the pressing of a key - mechanical, electromagnetic, etc. • On personal computers, when a key is depressed, an interrupt is generated and keyboard interrupt handler is started • The interrupt handler reads a hardware register inside the keyboard controller to get the number of the key (1 - 102) that was just depressed • When a key is released, a second interrupt is caused • Thus if a user depresses the SHIFT key, then depresses & releases the M key, then releases the SHIFT key, the operating system can see that the user wants an upper case “M”.

25. CRT Monitors Input / output • A monitor is a box containing a CRT (Cathode Ray Tube) and its power supplies. • The CRT contains a gun that can shoot an electron beam against a phosphorescent screen near the front of the tube. • Color monitors have three electron guns, one each for: • Red • Green • Blue

26. Flat Panel Displays Input / output • CRTs are far too bulky and heavy to be used in notebook computers • The most common screen for notebooks is based on the LCD (Liquid Crystal Display) tech. • Two types are common: • Passive matrix displays. • Active matrix displays

27. Mice Input / output • A mouse is a device for pointing at, and selecting items on a desktop • Low-level software in the computer accepts this information as it comes & converts the relative movements sent by the mouse to an absolute position on the screen. • When the user clicks a mouse button, the computer can figure out which item has been selected from knowledge of where the arrow is on the screen. • Four kinds of mice have been produced: • Mechanical mice. • Optical mice. • optomechanical • wireless mice

28. Modems Input / output • A computer device that uses the telephone lines to provide the underlying connectivity between computers • A raw telephone line is not suitable for transmission since it uses just 2 signals, 0 volts to represent a 0 and 3 to 5 Volts to represent a 1. • Two-level signals suffer considerable distortion when transmitted over a voice-grade telephone line, thereby leading to transmission errors

29. Modems - Carrier Input / output • A pure sine wave signal at a frequency of 1000 to 2000Hz, called a carrier, can be transmitted with relatively little distortion. • Because the pulsations of a sine wave are completely predictable, a pure sine wave transmits no information at all. • By varying the amplitude, frequency, or phase, a sequence of 1s and 0s can be transmitted • This process is called modulation

30. Modems - Modulation Time Tow-level signal Amplitude modulation Frequency modulation Phase modulation Input / output

31. Modems - Transmission Input / output • Modems can be: • Full-duplex: can transmit in both directions at the same time. • Half-duplex: can transmit in both direction, but once at a time. • Simplex: only transmit in one direction.

32. ISDN Input / output • Integrated Service Digital Network, is a standard for digital telephony • When the World Wide Web happened and people were clamoring for high-bandwidth digital access to the Internet, ISDN suddenly discovered its killer application • An ISDN line typically holds two independent digital channels at 64,000 bits/sec each, plus a signaling channel at 16,000 bits/sec. For businesses, a 30-channel ISDN line is typically used. • ISDN is faster than the analog channel and • Allows connection to be established in typically no more than 1 sec • No longer requires an analog modem, and • Much more reliable than an analog line.

33. ISDN for Home Use Input / output

34. DSL Input / output • Digital Subscriber Line • Technology for bringing high-bandwidth information to homes and small businesses over ordinary copper telephone lines • A DSL line carries both data and voice signals, where the data part is always connected • DSL uses the non-voice frequencies to transmit data, so the voice conversations are not affected by the data transmission

35. DSL - Advantages Input / output • The phone line can be used for phone calls while the internet is open • The speed is much higher than the regular modem • It doesn’t necessarily require new wiring, it can use the normal phone line • The company offering the DSL will provide the equipment as part of the installation

36. DSL - Disadvantages Input / output • The DSL connection works better when the user is closer to the provider’s central office • The connection is faster for receiving data than it is for sending data over the internet • The service is not available everywhere