Hardware Reference
In-Depth Information
PnP BIOS
Originally,installingandconfiguringdevicesinPCswasdifficult.Duringinstallation,the
user was faced with the task of configuring the new card by selecting the IRQ, I/O ports,
andDMAchannel.Inthepast,userswererequiredtomovejumpersorsetswitchesonthe
add-in cards to control these settings. They needed to know exactly which resources were
already in use so they could find a set of resources that did not conflict with the devices
alreadyinthesystem.Ifaconflictexisted,thesystemmightnotboot,andthedevicemight
fail or cause the conflicting hardware to fail.
PnP is technology designed to prevent configuration problems and provide users with the
capability to easily expand a PC. With PnP, the user simply plugs in the new card, and the
system configures it automatically for proper operation.
PnP is composed of three principal components:
• PnP BIOS
• Extended System Configuration Data (ESCD)
• PnP OS
The PnP BIOS initiates the configuration of the PnP cards during the bootup process. If
the cards previously were installed, the BIOS reads the information from ESCD, initial-
izes the cards, and boots the system. During the installation of new PnP cards, the BIOS
consults the ESCD to determine which system resources are available and needed for the
add-in cards. If the BIOS is capable of finding sufficient available resources, it configures
thecards.However,iftheBIOSisincapable oflocating sufficient available resources, the
PnP routines in the OS complete the configuration process. During the configuration pro-
cess, the configuration registers (in flash BIOS) on the cards and the ESCD are updated
with the new configuration data.
PnP Device IDs
All PnP devices must contain a PnP device ID to enable the OS to uniquely recognize the
devicesoitcanloadtheappropriatedriversoftware.Eachdevicemanufacturerisrespons-
ible for assigning the PnP ID for each product and storing it in the hardware.
Each manufacturer of PnP devices must be assigned an industry-unique, three-character
vendorID.Thenthedevice manufacturer isresponsible forassigning auniqueproductID
toeachproductmodel.AfteranIDisassignedtoaproductmodel,itmustnotbeassigned
to any other product model manufactured by the same company (that is, one that uses the
same vendor ID).
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