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Lesson 2Lesson 2

How Software and Hardware Work Together

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Slide 2Ver 1.0 10 April 2001

ObjectivesObjectives

Understand how the devices communicates

Introduction to system resources

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Slide 4Ver 1.0 10 April 2001

Interrupt RequestInterrupt Request

Device interruptCPU when it need CPU services usingINT wire

Eg When keyboard is pressed, INT wire is charged. The CPUstops what it is doing and run a BIOS routine (program) toquery the keyboard

To regulates data traffic on the I/O busThe adapter or unit on the I/O bus uses the interrupt to signalrequest to the CPU that it wants to send or receive data

Most IRQ wires are assigned to certain devices

16 IRQsOnly 15 IRQ can be used

IRQ 2 is wired to IRQ 9 (they are the same)

2 IRQ controllers, joined by IRQ 2 and IRQ 9

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Slide 5Ver 1.0 10 April 2001

IRQ ControllersIRQ Controllers

IRQ 8

IRQ 9 (dont exist)IRQ 10IRQ 11IRQ 12IRQ 13

IRQ 14

IRQ 15

IRQ 0IRQ 1

IRQ 2/9IRQ 3IRQ 4IRQ 5

IRQ 6

IRQ 7

IRQ2 join to IRQ9

Int

Intel CPU

IRQ Controller IRQ Controller

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Slide 6Ver 1.0 10 April 2001

Interrupt RequestInterrupt Request

Physically implemented as wiresIRQ 0, 1 and 8 are hard wired

IRQ is assigned to a device when the PC starts

Sharing of IRQ

PCI devices are able to shareConflict of IRQ

2 or more devices using the same IRQ

Devices with resources conflict will not work

Adjust resources to enable each device to have their

own resources

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Slide 7Ver 1.0 10 April 2001

IRQ TableIRQ Table

IRQ Devices

0 System timer

1 Keyboard controller

2 Open for use

3 COM 2, COM 4

4 COM 1, COM 3

5 LPT2 (printer)

6 Floppy drive controller

7 LPT1 (printer)

8 Real-time clock

9 Wired to IRQ 2

10 Open for use

11 Open for use

12 Open for use

13 Math coprocessor

14 Primary hard drive controller

15 Secondary hard drive controller

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Slide 8Ver 1.0 10 April 2001

I/O AddressI/O Address

CPU talks to devices using their I/O addressPhysically, it use a wire call IO/MEM

When voltage is placed on the wire, all devices listen. Thedevice will response if the I/O address matches

All devices have more than 1 I/O addressEg hard disk has preset I/O address 01F0-01FF

Sound card configures its own

2 devices cannot have the same I/O address

Once a device has an I/O address, no other device can

use itTwo ways communication: CPU and a device

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Slide 9Ver 1.0 10 April 2001

Physical wiring & HEXPhysical wiring & HEX

I/O address using 16 wiresDivided into 4 group of 4 wires (4groups x 4 wires)

Using 4 wires to representHexadecimal numbers (seetable)

Eg 01F0 is represented physicallyas:

0000 0001 1111 0000

Binary number Hex0000 All wire off 0

0001 Only 4th wire off 1

0010 Only 3rd wire off 2

0011 3th and 4th on 3

0100 Only 2nd wire on 4

0101 2nd and 4th wire on 5

0110 2nd and 3rd wire on 6

0111 Only 1stwire off 7

1000 Only 1stwire on 8

1001 1stand 4th wire on 9

1010 1st

and 3rd

wire on A1011 2nd wire off B

1100 1stand 2nd wire on C

1101 3rd wire off D

1110 4th wire off E

1111 All wires on F

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Slide 10Ver 1.0 10 April 2001

I/O Address TableI/O Address Table

IRQ I/O Address Device

0 040-05F System timer

1 060-06F Keyboard controller

2 0A0-0AF Access to IRQs above 7

4 3F8-3FFCOM1

3 2F8-2FF COM2

4 3E8-3EF COM3

3 2E8-2EF COM4

6 03F-3F7 Floppy

7 378-37F Parallel Port (LPT1)

14 1F0-1F7 Primary IDE

15 170-177 Secondary IDE

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Slide 11Ver 1.0 10 April 2001

Direct Memory AccessDirect Memory Access

Enables system to run background applicationwithout interfering the CPU

Creating background sounds in games

Access floppy disk drive

To increase system performanceFreed the CPU from handling data transfer tasks

PC has 2 DMA controllers, giving 8 channels0 to 7

Channel 0, 2, and 4 cannot be usedChannel 2 is used by Floppy disk drive

Device activate its assigned DMA channel if it wants to performa DMA data transfer

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Slide 12Ver 1.0 10 April 2001

Direct Memory AccessDirect Memory Access

Use by ISA devicesDMA is Slow

Not suitable for newer devices eg hard disk

Used by slow devices eg floppy drive, tape drive, sound card

Bus Master devicesSkip DMA totally

Popular in Hard disk, known as Ultra DMA

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Slide 13Ver 1.0 10 April 2001

Enabling DMA in Hard Disk (older HDD)Enabling DMA in Hard Disk (older HDD)

Steps:Control Panel

Double-Click System applet

Click Device Manager

Double-click on Disk Drive

Click on selected hard disk

Click on Properties

Click on the Setting tab

Check the DMA box

Note: If problem is encounteredafter enabling DMA, remove thesetting in SAFE MODE

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Slide 14Ver 1.0 10 April 2001

DMA ChannelsDMA Channels

DMA Channels Function Other Users

0 Memory Refresh None

1 Open for Use SCSI, ECP port

2 Floppy drive controller Tape

3 Open for Use ECP port SCSI card,Network Card

4 Not Available Cascade to 0-3

5 Sound Card SCSI

6 Open for Use Sound Card, NIC

7 Open for Use Sound Card, NIC

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Slide 15Ver 1.0 10 April 2001

Device Manager to Find Resources AllocationDevice Manager to Find Resources Allocation

The steps are:Control Panel

System Applet

Device Manager tab

Double-click on Computer