1. Expansion Bus
Chapter 5

2. Overview In this chapter, you will learn to
Identify the structure and function of the expansion bus
Explain classic system resources
Identify the modern expansion bus slots
Install expansion cards properly
Troubleshoot expansion card problems
Teaching Tip
When gaining attention and establishing common ground, ask questions of the class such as, “Who here has installed an expansion card?” or “Who here has ever dealt with IRQs?”
For a positive statement, tell the class, “In this lesson, we are going to learn how to recognize various buses and install cards, and then configure the PC for these cards.”

3. Structure and Function of the Expansion Bus

4. Connections
Expansion slots connect to both the Northbridge and Southbridge

5. System Crystal
All integrated circuits must be regulated by a clock crystal
Every device soldered to the motherboard is designed to run at the speed of the system crystal

6. Expansion Bus Crystal
The expansion bus crystal is an extension to the external data bus
Used to control the part of the external data bus connected to the expansion slot
The chipset acts as a divider between the two buses, compensating for the speed difference with wait state and special buffering areas.

7. CPU Crystals
The first bus is the frontside bus that runs at the speed of the system crystal
The second bus is the expansion bus that runs at the speed of the expansion bus crystal

8. PC Bus (8-bit ISA)
IBM XT had 8088 processor and an 8-bit external data bus at a top speed of 4.77MHz
IBM used an expansion bus that could run around 7 MHz (as fast as the system bus) called the PC bus, XT bus, or ISA bus
Many people consider the failure of Apple to allow third parties to copy its expansion bus at no cost one of the main reasons PCs are more popular than Apple computers.
The A+ Certification exams refer to these early buses as ISA.

9. AT Bus (16-bit ISA)
The AT bus is a 16-bit bus running at a speed of 8.33 MHz and is created by adding a set of connections to the end of the PC bus
The PC/XT and AT buses are also known as the 8-bit ISA and 16-bit ISA respectively

10. System Resources

11. System Resources
Expansion cards and the CPU need some way to communicate
System resources help to define how to communicate:
I/O addresses
IRQs
DMA channels
Memory addresses

12. Who’s Who?
How does a device know that the CPU wants its attention?

13. I/O Mem Wire
The expansion bus consists of the external data bus and the address bus
Every device on the PC connects to both
When a voltage is placed on the IO/MEM wire, only the first 16 wires are monitored by all devices
You won’t find an IO/MEM wire on a modern CPU as this process is now a bit more complex, but the concept hasn’t changed one bit!

14. I/O Addresses
Different wire patterns used by the CPU to communicate with different devices inside the PC are known as I/O addresses
The more complex the device, the more I/O addresses it uses.
Don’t be surprised on the A+ exams if you’re asked about seemingly three-digit I/O addresses, such as 3F8. Just tack on the leading zero and you’re in sync with the I/O address map.

15. Device Manager
Device Manager allows you to see what resources are being used by your devices
Alt-click My ComputerPropertiesHardware tab Device Manager button

16. Viewing Resources
Device Manager  Click “+” next to device  double-click device Resources tab
To get to Device Manager, alt-click My Computer and choose Properties Hardware tab Device Manager

17. I/O Addresses Use Hexademimal
Before we can talk about I/O addresses we need to understand hexadecimal and binary math
For an in-depth discussion of binary
and hexadecimal numbering systems,
click here

18. I/O Addresses
I/O addresses are represented as 4-digit hexadecimal values starting from 0000 and ending at FFFF
Remember that when the CPU turns on the IO/MEM wire, it sends and I/O address using the first 16 address bus wires
These wires either have a voltage (1) or they don’t (0)
We represent which wires have a voltage with an address bus binary number with 16 digits
Wouldn’t it be easier to represent this long binary number with the hexadecimal number 2BAD? That’s exactly what computer techs do!

19. Rules of I/O Addresses All devices must have an I/O address
This is how the CPU talks to everything in the PC
The I/O address is either preset or must be assigned
All devices use more than one I/O address
CPU uses different I/O addresses for different commands
Devices must be able to respond to the CPU with other I/O addresses
Hence, a range of I/O addresses is assigned
No two devices can share the same I/O address

20. I/O Address Terminology
When talking about I/O addresses, drop the leading zeros (1F0…not 01F0)
Every device gets a range of I/O addresses
The first I/O address is called the base I/O address
Put an “h” on the end of the value to specify hex (1F0h)
I/O addresses provide a two-way communication pathway between the peripherals and the CPU
Discussion Point
Base Hex
In keeping with all things tech, hex needs its own tech talk. We rarely talk about the entire I/O address range, just the first I/O address. If that hex number has any leading zeros, we generally drop those. When this is done, we generally add a lowercase “h” to the end of the number to indicate the leading zeros.
In other words, if an I/O address range for COM1 is 03F8 to 03FF, techs will generally only talk about the first I/O address (03F8), and then go one step further by dropping the leading zero of the first I/O address and adding an “h.”
So, COM1’s I/O range of 03F8 to 03FF becomes 03F8, and then it becomes the base hex of 3F8h. The original 16-bit binary number still remains , whether it is represented as 03F8, 3F8h, or 3F8. Fun, eh?

21. Interrupts The CPU can initiate a conversation with any device at will
Any device may talk to the CPU but how does a device get the CPU’s attention?
Devices use the interruption mechanism to gain the attention of the CPU by placing a voltage on a special wire called the INT (interrupt) wire – the CPU will stop what it is doing and deal with the device

22. The Original 8259 Chip
The 8259 chip acts as an intermediary between all the devices and the CPU’s INT wire
It hooks to the INT wire of the CPU on one side, and has 8 other wires called the interrupt requests (IRQs) that extend out from the chip into the motherboard

23. IRQs for the System Timer, Keyboard, and ISA Slots
Every device has an IRQ
The system timer, keyboard controller, and ISA slots are shown

24. Cascaded 8259s
The 8259 chips were designed to run in a cascade to provide more IRQs
IRQs 2 and 9 are the same and referred to as IRQ2/9

25. 16-Bit IRQ Map Discussion Point IRQ Order of Precedence
IRQ numbers have an order of priority. This means that if two devices needed some CPU attention at the same time, the device with the lower number had the priority and got the attention first.
When the second interrupt controller chip was added, things changed a bit. Because IRQ2 was already generally reserved, they made it a redirect (or cascade) to the second controller. Not only is IRQ2 no longer used as an IRQ, but the order of precedence is redirected, too. Anything set to use IRQ2 is really using IRQ9, whether it knows it or not. As such, you cannot have IRQ2 and IRQ9 assigned at the same time. IRQ2 is generally called IRQ2/9.
The order of precedence in modern PCs is as follows: 0, 1, 8, 9, 10, 11, 12, 13, 14, 15, 3, 4, 5, 6, and 7. IRQ2 is not in the list; all the IRQs on the second controller fall where IRQ2 was.
Separate IRQ2 and IRQ9 don’t exist; instead, it is called iRQ2/9.
You should know the traditional 16-bit ISA IRQ map.

26. The Rules of IRQs Every device needs an IRQ
Joysticks do not use interrupts (there’s always an exception!)
No two devices can share an IRQ
What happens if they do?
Could two devices exist using the same interrupt?
Tech Tip
Cutting-edge IRQ Handling
Modern systems assign most IRQs automatically through a mechanism called Plug and Play, but may use either of two interrupt controllers: the 8259 Programmable Interrupt Controller (PIC) or the Advanced Programmable Interrupt Controller (APIC). Which controller is used and how it affects device installation depend greatly on the specific motherboard, expansion devices, and operating system installed. I’ll go through all of this, but you need more information first for any of it to make sense on a technology level. From a practical standpoint, though, even the latest and greatest expansion card requires an IRQ and can run into conflicts with other devices in the system. Although you can find five or more devices seemingly sharing the same IRQ and all running just fine, you can also find two devices sharing an IRQ and causing conflicts. You need to understand the old way before these new conflicts make sense. The old stuff won’t die!

27. COM and LPT Ports Every peripheral needs an IRQ and I/O address
IBM created standard preset combinations of IRQs and I/O addresses
These preset combinations for serial devices and parallel devices are called COM ports and LPT ports respectively
COM1 uses IRQ 4
COM2 uses IRQ 3
LPT1 uses IRQ 7
LPT2 uses IRQ 5

28. COM and LPT Ports
COM3 and COM4 are two common port standards that are assigned the 3E8-3EF and 2E8-2EF set of I/O addresses respectively
COM3 uses IRQ4 and COM4 uses IRQ3
These are the same IRQ’s used for COM1 and COM2
How can two devices use the same IRQ…as long as they never talk at the same time!
LPT (Line Printer) port settings apply to parallel connections for devices such as printers

29. COM Port Assignments
Because technicians need to be able to support older devices, the A+ Certification exams expect all A+ certified techs to know the COM and LPT resource assignments. In other words, memorize the chart!

30. Physical vs. I/O Ports I/O ports:
A serial port is a 9 or 15-pin male DB connector, whereas the COM port is just the I/O address and IRQ assigned to it
A parallel port is a 25-pin female DB connector, whereas the LPT port is just the IRQ and an I/O address assigned to it
Tech Tip
COM Ports
Serial ports that have system resources assigned using one of the COM combinations often get shorthanded as COM ports. This can cause some confusion for techs who don’t understand what’s happening behind the scenes. When you assign COM1 to serial port 1 in the CMOS setup utility, you have assigned both a range of I/O addresses and an IRQ to that serial port. You know from Table 6.4 that you shouldn’t turn around in the same system and assign the modem COM3, right? This would create a classic IRQ conflict and lead to system instability. Further, many manufacturers create devices that can use nonstandard combinations of I/O addresses and IRQs, such as a modem that uses 03E8 as the base I/O (and thus is referred to as COM3), but then uses IRQ2 rather than IRQ4 to avoid a conflict with any device assigned COM1 resources. Knowing the combinations referred to by COM1, COM2, and so on—and the possible variations—helps you troubleshoot simple errors.

31. COM Ports and LPT Ports Today
IBM dictated a specific I/O address and IRQ for a particular COM or LPT port
The IRQ can be changed as long as the device can handle it, and the software that communicates with the device knows about the change
Change COM or LPT IRQs in the CMOS setup

32. Direct Memory Access (DMA)
Direct Memory Access (DMA) is the process of accessing memory without using the CPU
It enables the system to run background applications without interrupting the CPU

33. The 8237 Chip The 8237 chip is used to control DMA functions
It links to the CPU via a HRQ wire
The chip has 4 wires, called DMA requests (DRQs) or DMA channels, which lead to the DRAM refresh circuitry and ISA slots
No two devices can share DRQs

34. Cascaded 8237 Chips Provides up to 7 DMA channels
DRQ0 and DRQ4 are linked
DMA channels 1 thru 3 are for 8-bit transfers
DMA channels 5 thru 7 are for 16-bit transfers
Designed for the ISA bus
Discussion Point
DMA Controller Chips
DMA controller chips, like interrupt controllers, are generally found as a cascading pair. Each DMA controller has four DRQs. When cascading the two controllers, you lose one controller as the redirect and end up with a total of seven available DRQ numbers. DRQ0 cascades to DRQ4 (DRQ0/4) and is generally referred to as simply DRQ0.

35. DMA Assignments

36. Bus Mastering
Bus masters are devices that use the DMA without accessing the 8237 or CPU
They have a circuitry that allows them to watch for other devices accessing the external data bus
No two devices can use the external data bus at the same time
Bus mastering is extremely popular in hard drives
All EIDE hard drives take advantage of bus mastering
Sound cards and floppy drives still use the old DMA

37. Modern Expansion Bus

38. Microchannel Architecture (MCA )
MCA had a 32-bit bus to match the 386 CPU’s external data bus with a speed of 12MHz
May self configure devices
IBM proprietary and expensive

39. Enhanced ISA (EISA )
EISA (EE-sah) was a 32-bit self-configuring expansion bus that was cheaper than the MCA
Used a unique double-slot connector compatible with ISA devices

40. VESA VL-Bus
The Video Electronics Standards Association (VESA) created the VESA local (VL) bus to solve the problems of speed and throughput
Speed of 33 MHz
Paired with an ISA slot typically
Controlled only the functions specific to VL-bus devices…relying on the ISA slot for basic control functions
The A+ Certification exams do not cover MCA, EISA, and VL-Bus expansion buses. I’ve included them here for completeness.

41. PCI
Peripheral Component Interconnect (PCI) provides a stronger, faster, and flexible alternative to any other expansion bus
The flexible design enables the PCI to coexist with other buses, and scale up in speed and throughput
PCI devices are self-configuring
PCI Special Interest Group (SIG) defined I/O addresses and IRQs for most devices…using a sharable Interrupt Channel instead of IRQs
Fully implements DMA – allowing PCI devices to transfer data among themselves

42. PCI
Bus mastering enables the PCI devices to transfer data between themselves
Its burst mode feature enables efficient data transfers
Combo Boards
It often surprises folks how long dying technology lingers on computers. A trip to the computer store even as late as the summer of 2003 as I’m writing this reveals newly manufactured PCI/ISA combo motherboards. Certainly, you’ll find such boards in millions of functioning PCs across the globe.
Not all PCI cards play well together! Most do, but occasional resource conflicts are inevitable given the incredible variety and number of PCI expansion cards available. You’ll learn more about this in the “Installing Expansion Cards” section that follows.

43. PCI Divides its chipset duties between two chips
Northbridge (or PCI controller) performs the classic functions and controls the PCI bus
Southbridge (PCI to ISA bridge or just PCI bridge) acts as an intermediary between the PCI bus and the other bus

44. AGP
AGP is a brown colored connector found on modern motherboards and is used for inserting video cards

45. Installing Expansion Cards

46. Steps to Installing Expansion Cards
Knowledge
Physical installation
Assigning resources to the card
Device drivers
Verify
Tech Tip
Installation Order
Some manufacturers insist on a different order for device installation than the traditional one listed here. The most common variation requires you to install the drivers and support software for an expansion card before you insert the card. Failure to follow the manufacturer’s directions with such a card can lead to hours of frustration while you uninstall the card and reinstall the drivers, sometimes manually removing some drivers and software from the system. Bottom line? Read the instructions that come with a particular card! I’ll provide more specific examples of problem devices in later chapters.

47. Step 1: Knowledge Learn about the device by reading the documentation
Do you have device drivers for your operating system (with Windows 98 and later you usually do)
Does the device work with your operating system?
Check the Hardware Compatibility List for Windows 2000 or XP
Devices on this list have been certified by Microsoft to work with Windows
The Windows installation CD contains the HCL, or you may get the latest version on Microsoft’s web site at

48. Step 2: Physical Installation
Install the card
Hold the card on its edges – don’t touch connectors or the components on the card
Insert at the proper angle
Use the connection screw which helps to ground the card
Use proper ESD procedures

49. Step 3: Assigning Resources
Every expansion card must have system resources assigned to it
Every PCI motherboard and card can use Plug and Play
Some of the later ISA cards were Plug and Play-capable
But sometimes Plug and Play doesn’t work properly, so every good tech needs to know how to troubleshoot it

50. PnP (Plug and Play)
PnP consists of a series of standards designed to enable self-configuration of devices
Devices that do not support PnP are called legacy devices
The PnP standard lumps I/O addresses, IRQs, and DMA together under the term “system resources.” For example, the system resources for the floppy drive are I/O addresses 3F0–3F7, IRQ6, and DMA channel 2.

51. PnP Requirements PnP BIOS PnP Operating System PnP device
All Pentium and later computers have a PnP BIOS
PnP Operating System
Windows 95 or later
PnP device
No one makes non-PnP devices anymore

52. PnP BIOS

53. Legacy Devices in the CMOS
System resources refers to I/O addresses, IRQs, and DMA used

54. Legacy Devices have Jumpers

55. How PnP Works
Initially PnP devices remain quiet while the BIOS determines resources required by legacy devices
Discussion Point
The PnP Process Simplified
When the computer boots, the BIOS performs many functions. After completing the POST (power on self test), but before loading the bootstrap program (which loads the operating system), the PnP BIOS takes over and tells all PnP devices to “be quiet” so all the legacy (non-PnP) devices can be found. After determining what systems resources (I/O, IRQ, and DMA allocations) are left over after the legacy device resources have been assigned, the PnP BIOS then matches the PnP devices with the available system resources. The PnP BIOS then assigns these resources to the PnP devices as needed. These assignments are permanent only for this boot. They may be changed on the next boot depending on the configuration of the PC at that time and the needs of the devices on the next boot.

56. How PnP Works
A legacy device list is created to reserve those system resources
IRQ steering can cause problems among PCI cards, even on systems with no legacy cards at all, although it’s rare.

57. How PnP Works
Next the PnP BIOS checks with the PnP devices to see which system resources are options for each device

58. How PnP Works
The PnP BIOS then assigns system resources based on that information

59. Step 4: Device Drivers
All devices require BIOS, which for expansion cards is almost always a device driver
Devices will come with device drivers on the installation CD
It is recommended that you get the latest drivers from the manufacturer’s web site
To update the device drivers you may need to uninstall the current driver first
Windows XP has a feature to rollback your system to the previous driver just in case the new driver you installed does not work

60. Updating the Driver
Alt-click on the device in Device Manager and choose Update Driver…
Choose Uninstall to remove the current driver
Tech Tip
Beta Drivers
Many PC enthusiasts try to coax the most possible performance out of their PC components, much like auto enthusiasts will tinker with engine tunings to get a little extra horsepower out of their engines. Expansion card manufacturers love enthusiasts, who often will act as free testers for their unpolished drivers, known as beta drivers. Beta drivers are fine for the most part, but sometimes can cause amazing system instability— ever a good thing! If you use beta drivers, make sure you know how to uninstall or roll back to previous drivers!

61. Driver Rollback
Alt-click the device in Device Manager and choose Properties, then the Driver tab

62. Step 5: Verify
Check the device properties in Device Manager to verify it is working properly

63. Troubleshooting Expansion Cards

64. Device Manager Check for the device in Device Manager
Alt-click My ComputerProperties Hardware tab Device Manager
If the device does not show up in Device Manager
Run the Add/Remove Hardware Wizard in Control Panel
If it still doesn’t show up, the device is damaged or it is a legacy device whose system resources are not configured properly
Windows NT 4.0 does not have a Device Manager. The only way to verify whether or not a device works is to give it a whirl!

65. Device Manager Symbols
Black ! on a yellow circle
Device is missing, Windows doesn’t recognize it, or a device driver problem – device may still work
Red X
Disabled device – system resource conflict or damaged device – will not work
Blue I on a white background
System resources were configured manually
Green ?
Windows does not have the correct driver but has successfully installed a compatible driver

66. Rules for Device Installation
Installing legacy devices:
Run the Device Manager to determine the available resources for the system
Configure the device to use the resources
You may need to set jumpers, flip switches, or run a special setup program
Run the Add/Remove Hardware Wizard to inform Windows of the legacy device

67. Device Manager Sorted by IRQ

68. Changing the Resources
The Resources tab of the device Properties sheet show which resources Windows has assigned
You may use the automatic settings, or uncheck the box and click Change Settings to manually specify settings to use
Exercise
Examining System Resources
Let the students use the Device Manager to examine system resources for various devices.
Troubleshooting
Set up some errors for the students to troubleshoot. You can misconfigure some parts while the students are on a break, and have them boot the computers, diagnose, and fix the problems. Try setting two devices to the same IRQ, misconfiguring the modem to the wrong port, or loading the wrong driver for a device.

69. Legacy Setup Software Program

70. PCI-X and PCI-Express

71. PCI-X PCI-X is a huge advancement to PCI Fully backward compatible
Uses the same connectors, so it will accept standard PCI cards
32-bit and the more common 64-bit versions
Much faster with four speed grades
PCI-X 66
PCI-X 133
PCI-X 266
PCI-X 533
Parallel interface like PCI

72. PCI-Express More revolutionary than evolutionary Serial interface
Not hardware compatible
Software compatible
Flexible, scalable, native hot swap/hot plug capable
Very fast at 2.0 Gbps for each lane between the controller and the device
May use up to 32 lanes for a maximum bandwidth of 128 Gbps

74. Hexadecimal
Hexadecimal, or base 16-bit mathematics, is a shorthand method of describing a series of binary values
Hex (6) + decimal (10) = hexadecimal (16)
Our decimal numbering system is based on 10
We use ten digits: 0,1,2,3,4,5,6,7,8,9
Examples: 456, 187, 23, 7
Binary numbering systems are based on 2
We use two digits: 0,1
Examples: 101, 110, 1,
Hexadecimal numbering systems are based on 16
We use 16 digits: 0,1,2,3,4,5,6,7,8,9,A,B,C,D,E,F
A =10, B=11, C=12, D=13, E=14, F=15
Examples: 6B7, ABCD, 123, FFFF, 6

75. Writing Numbers Decimal Binary Hexadecimal
Each digit as you move to the left is worth 10 times as much as the one before it
In the number 456, the 6 is in the 1s column, the 5 is in the 10s column, and the 4 is in the 100s column
Binary
Each digit as you move to the left is worth 2 times as much as the one before it
In the number 456, the 6 is in the 1s column, the 5 is in the 2s column, and the 4 is in the 4s column
Hexadecimal
Each digit as you move to the left is worth 16 times as much as the one before it
In the number 456, the 6 is in the 1s column, the 5 is in the 16s column, and the 4 is in the 256s column

76. Digit Values
Digit values as you read from the left-most digit (4th digit) to the right-most digit (1st digit):
Decimal
104 =
10,000
103 =
1,000
102 =
100
101 = 10
100 = 1
Binary
24 = 16
23 = 8
22 = 4
21 = 2
20 =
Hexa-decimal
164 =
16,536
163 =
4,096
162 =
256
161 =
160 =

77. Equating Hexadecimal and Binary Numbers1
1001 9 10 2
1010
A (10) 11 3
1011
B (11)
100 4
1100
C (12)
101 5
1101
D (13)
110 6
1110
E (14)
111 7
1111
F (15)
1000 8

78. Converting from Binary to Hexadecimal
To convert from binary to hexadecimal, separate the binary number into groups of 4 digits starting from the right
We can add as many zeros to the front of the number as we need to
Then convert each set of four digits to its hexadecimal value
0011 = = = = 11
So the hexadecimal equivalent is 356B
Remember that 11 is represented by a B in hexadecimal

79. Converting from Hexadecimal to Binary
To convert from hexadecimal to binary, expand each hexadecimal number into its 4-digit binary equivalent
356B becomes 0011 (3) 0101 (5) 0110 (6) 1011 (B) or
But we can leave the two leading zeros off:
Click here to return to our discussion about I/O Addresses