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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