Post on 13-Dec-2015
Riyadh Philanthropic Society For Science
Prince Sultan College For WomanDept. of Computer & Information Sciences
CS 251Introduction to Computer Organization
& Assembly Language
Lecture 9(Computer System Organization)
Input / Output
Input / output 2
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
Outline
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Introduction
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.
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Logical Structure of PCs
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.
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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
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I/O Mechanism – Port mapped
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
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I/O Mechanism – Memory Mapped
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
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I/O Mechanism – DMA
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
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Interrupt
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.
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Bus Arbiter & Cycle Stealing
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
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Buses
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
of information being communicated
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Bus Interconnection Scheme
memory I/O
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Data Bus
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.
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Address Bus
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)
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Address & Data Groups
often bundle address and data signals separately and use different physical
pathways
may multiplex using same physical pathway
1
0address
1
0data
1
0address data
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Common Control Signals
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
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Bus Protocols
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.
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Synchronous Memory Read
T1 initiate memory read (address, mem read signal)
T2 time for memory to do internal work
T3 data ready for reading from bus
T1
stable data
T2 T3
clock
addrs stable address
mem read
data
Assumption:Sensing of bus signals done during clock trailing edge
Input / output 19
Asynchronous Memory Writeno shared clock pacing the protocol mem write command
proc
esso
r
Memory sends signal that it has finished writing.
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ISA, EISA & PCI Buses
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
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Typical Modern PC
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Typical Modern PC (Cont.)
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.
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Terminals
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.
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Keyboards 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”.
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CRT Monitors
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
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Flat Panel Displays
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
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Mice 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
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Modems
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
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Modems - Carrier
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
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Modems - ModulationTime
Tow-level signal
Amplitude modulation
Frequency modulation
Phase modulation
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Modems - Transmission
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.
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ISDN
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.
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ISDN for Home Use
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DSL
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
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DSL - Advantages
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
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DSL - Disadvantages
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