The expansion bus
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The Expansion Bus. Three Tasks. A card needs to be built specifically for the expansion slot – the right signals at the right place. Connectivity Card needs some way to communicate with the CPU – in and out. Communication

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Three tasks
Three Tasks

  • A card needs to be built specifically for the expansion slot – the right signals at the right place. Connectivity

  • Card needs some way to communicate with the CPU – in and out. Communication

  • Operating System needs some way to allow user to control the device/card. Drivers


  • Expansion bus(es) connect to the chipset

And PCIe


  • CPU (and Northbridge) tied to System Crystal

  • Almost all chips/devices have clock wire for timing

  • This could lead to lots of devices at each specific speed (66, 100, 133, etc.)

  • Solution is to add an Expansion Crystal for consistent timing on the bus

Errata to book
Errata to Book

  • Figure 8-5 shows Expansion Crystal connected to CPU. That is not correct.

  • Expansion Crystal should connect to Sound Card and Modem Card (which figure does not show)

Pc bus
PC Bus

  • Was an 8-bit bus (match to EDB)

  • Ran at about 7 MHz

  • Had patents, but no licensing fees

  • Did not, of itself, create clone market as Michael suggests.

  • Also did not mess with Apple as he suggests

286 at 16 bits
286 at 16 bits

  • Need to improve on 8-bit expansion bus

  • Just extend the bus to add more bits

  • Still running at 7 MHz

System resources
System Resources

  • I/O Resources

  • IRQ’s

  • DMA channels

  • Memory Addresses

  • Our life today, with Plug and Play (PnP), takes care of most of this for us

I o addresses
I/O Addresses

  • Input/Output Port Addresses

  • Use the IO/MEM wire with addresses

  • CPU Device

  • We use hex notation, using four hex digits. Range is 0000 to FFFF

  • Not every device has four I/O addresses; some have more, some less

I o addresses for devices
I/O Addresses for Devices

  • Digging into Device Manager:

Rules of i o addressing
Rules of I/O Addressing

  • All devices have at least one I/O address

  • Most devices use more than one address (system speaker only uses one)

  • No two devices can share the same I/O address

  • The first address in the range is often called the Base Address, 01F0h for hard disk drive

Interrupt requests irqs
Interrupt Requests (IRQs)

  • We need a way to start communication with the CPU from the device

  • We use Interruption, much like a ringing telephone

  • Interrupts are CPU Device

I/O Advanced Programmable Interrupt Controller (IOAPIC)

Irq rules
IRQ Rules

  • Almost every device needs an IRQ (joystick does not use one)

  • Mostly, can’t share an IRQ (modem/fax can)

  • Many IRQs are allocated to devices through a table of standard values

Direct memory access dma
Direct Memory Access (DMA)

  • Most of the time, the CPU is busy and much of the system is idle

  • CPU uses EDB about 5 percent of the time

  • Some devices can access memory directly without the CPU’s help

  • Sound cards, floppy drives and hard disk drives use DMA

  • Used a very simple, “extra” CPU with DMA Request, or Channel wires

Limits to dma
Limits to DMA

  • Designed for PC bus, limited to 7 MHz

  • Can only handle 8-bit data streams per chip

  • Cascading chips allow for 16-bit transfers

  • Now used for low-speed data transfers: floppy drive (DRQ2), sound and tape backup

  • Today we have Bus Mastering; the device takes (intelligent) control and skips the DMA chip giving us Ultra DMA

Memory addresses
Memory Addresses

  • Option ROM (from previous week) on the card needs memory address space

  • Usually allocated from near the top of first meg of RAM (Upper Memory)

  • Devices can not share memory

  • Ranges can not overlap

  • Fully automatic today

New expansion bus
New Expansion Bus

  • 16-bit bus only ran at 7 MHz and was limited to 16 bits at a time

  • We had to manually assign System Resources to each card

  • We needed improved technology and a way to go faster

False starts part 1
False starts – Part 1

  • IBM and Microchannel Architecture (MCA) – first 32-bit bus

  • Smarter bus – could allocate System Resources

  • Required “personality disk” to install or remove – giant hassle over floppies

  • Heavily patented and expensive licenses

  • Used on PS/2 line (‘87-’88) from IBM

Spin doctors
Spin Doctors

  • Industry (and consumers) resisted MCA

  • Manufactures argued for “Return to Industry Standard Architecture” or ISA Bus (ii-sa)

  • 1987-1988 time frame


False starts part 2
False starts – Part 2

  • EISA bus (ee-sa)

  • Used a double-deep slot; top part for ISA cards and lower, 32-bit slot for EISA cards

  • Lasted almost a year

ISA contacts here

EISA contacts here

False starts part 3
False starts – Part 3

  • Video Electronics Standards Association created the VESA local bus (VL-bus)

  • 32-bits total (16+16); connected at Front Side Bus; ran at 33 MHz

  • “Glue on” to ISA bus

Enter pci
Enter PCI

  • Intel gets credit for this one (1993)

  • Peripheral Component Interconnect

  • 32-bit, 33 MHz; “mezzanine” bus as it sits between FSB and rest of expansion bus (ISA)

  • Self-configuring (PnP), allows Ultra-DMA (bus mastering)

  • Uses sharable Interrupt Channels (INTA, INTB, C and D)

  • Supports I/O addresses above 3F8 to FFFF

Honorable mention to agp
Honorable Mention to AGP

  • Video demands keep pushing bus improvements

  • Accelerated Graphics Port

  • PCI slot with its own connection to Northbridge

  • This, and more, when we do Video chapter


Pci x

  • PCI Extended

  • 64-bit slot for servers, Mac G5

  • Four speeds: 66, 133, 266 and 533. 266 is double-pumped 133; 533 is quad-pumped.

  • Not going to see this on the desktop.

Pci express
PCI Express

  • PCIe –xN. PCI express by “N” (some number of lanes wide). About 2004-5

  • Serial connection (differential signals)

  • Not a shared bus like all before it; each connection direct to Northbridge chip

Installing expansion cards
Installing Expansion Cards

  • Need to know that the card works with OS and motherboard

  • Insert card properly – don’t break things and beware of ESD

  • Provide drivers – specific to card and OS

  • Verify proper operation

Installation order
Installation Order

  • Most video cards today require that you

    • uninstall current video drivers (revert back to generic Microsoft driver)

    • install new driver software

    • Remove old card and install new card

    • Finish (driver) installation

  • Always read installation instructions first

Will it work
Will it work?

  • Will it work with your motherboard?

    • Can’t install PCIe-x16 video card in AGP slot

    • Can’t install ISA sound card in PCI-only m/b

  • Will it work with your OS?

    • This will be an issue for Windows 7 (?)

    • Always an issue with new OS

  • Is device on the Hardware Compatibility List (HCL) or Windows Marketplace?

Physical installation
Physical Installation

  • Do you have an available slot?

  • Beware ESD

  • Beware the 5v on the motherboard – pull the plug during installation

  • Handle the card carefully – don’t get “wet” fingerprints on connector.

  • Insert, and remove, card at a slight angle

  • Install the attachment screw before you power up the system

Preventative maintenance
Preventative Maintenance

  • Don’t use pencil eraser to “clean” contacts, rather, use canned contact cleaner – but only if card has had a long shelf life.

  • Sometimes removing and reseating a card a time or two will bring the card back to life.

  • The attachment screw WILL line up with hole if you have installed card correctly



  • Expansion cards WILL have a floppy/CD with driver(s) in the box.

  • Read the directions to determine what’s first: device install or driver install

  • Video cards usually need old (card) drivers removed first; usually in Add/Remove Programs

  • Remove All-In-One printer controls from Add or Remove Programs too.

More drivers
More Drivers

  • A lot of drivers are “unsigned” – usually means they did not pay Microsoft to test the driver. It’s not as scary as it looks.

  • If you have to force the Add Hardware Wizard you probably did something wrong

  • 64-bit Vista and 7 require driver signing

Verify operation
Verify Operation

  • Don’t leave until you have verified operation of the expansion card.

  • Device Manager is a good place to check after install and driver install

  • Have the device do its something just to make sure all is well (and client is happy)


Plug and play pray
Plug and Play (Pray)

  • Need a PnP BIOS – standard issue since about 1997

  • Need a PnP OS – Windows 9x and up, not DOS or Windows 3.x

  • Need a PnP device/card – all new (PCI and up) cards are PnP. Some ISA cards were also. Not marked on box anymore.


How pnp works
How PnP works

  • PnP devices told to be quiet

  • BIOS searches for legacy devices and assigns resources

  • PnP devices announce usable resources

  • BIOS allocates resources to PnP card(s)

  • This happens each time you boot system and occurs prior to beep.



  • BIOS keeps list of devices in Extended System Configuration Data list

  • Usually, at boot, this list is checked against installed hardware and if they match, the allocation process is skipped


Irq steering
IRQ Steering

  • PCI devices use dynamically assigned interrupt channels rather than IRQs.

  • Sometimes we have to make it appear that device is using IRQ; often we “stack” devices on single IRQ.

  • The BIOS sorts all this out and will “switch” resources for a legacy program.


Trouble visable
Trouble - Visable

  • Device Manager error indicators:

    • Yellow circle with black exclamation point usually means driver is damaged

    • Red “X” symbol means device is disabled and not working

    • Yellow question mark is found device but lacking correct driver(s).



Trouble not visible
Trouble – Not Visible

  • Windows should recognize new card on bootup and ask for driver(s). If it does not ask, you (or card) failed some step.

  • USB devices should be recognized on connection.

  • Drivers, drivers, drivers

  • Get an account at