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Micro House PC Hardware Library Volume II: Network Interface Cards And Modems Micro House PC Hardware Library Volume II: Network Interface Cards And Modems
by Micro House International, Inc. and Scott Mueller
Que, Macmillan Computer Publishing
ISBN: 078971664x   Pub Date: 06/17/98
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The Hardware Component

The hardware component refers to both computer systems and adapter cards. The term does not mean, however, that you cannot use your older ISA adapter cards (referred to as legacy cards) in a PnP system. You can use these cards; in fact, your PnP BIOS automatically re-assigns PnP-compatible cards around existing legacy components.

PnP adapter cards communicate with the system BIOS and the operating system to convey information about what system resources are needed. The BIOS and operating system, in turn, resolve conflicts (wherever possible) and inform the adapter cards which specific resources it should use. The adapter card then can modify its configuration to use the specified resources.

The BIOS Component

The BIOS component means that most users of older PCs need to update their BIOSes or purchase new machines that have PnP BIOSes. For a BIOS to be compatible, it must support 13 additional system function calls, which can be used by the OS component of a PnP system. The PnP BIOS specification was developed jointly by Compaq, Intel, and Phoenix Technologies.

The PnP features of the BIOS are implemented through an expanded POST. The BIOS is responsible for identification, isolation, and possible configuration of PnP adapter cards. The BIOS accomplishes these tasks by performing the following steps:

1.  Disable any configurable devices on the motherboard or on adapter cards.
2.  Identify any PnP PCI or ISA devices.
3.  Compile an initial resource-allocation map for ports, IRQs, DMAs, and memory.
4.  Enable I/O devices.
5.  Scan the ROMs of ISA devices.
6.  Configure initial-program-load (IPL) devices, which are used later to boot the system.
7.  Enable configurable devices by informing them which resources have been assigned to them.
8.  Start the bootstrap loader.
9.  Transfer control to the operating system.

The Operating-System Component

The operating-system component can be implemented by most newer systems, such as OS/2, Windows 95, or DOS extensions. Extensions of this type should be familiar to most DOS users; extensions have been used for years to provide support for CD-ROM drives. Extension software is available now for existing operating systems, and you can expect all new PC operating systems to have PnP support built in. If you are using Windows NT 4.0, PnP drivers may or may not have been loaded automatically. If not, the driver can be found on the NT 4.0 CD in the DRVLIB\PNPISA\ directory. Open the correct sub-directory for your chipset and install the file PNPISA.INF.

It is the responsibility of the operating system to inform users of conflicts that cannot be resolved by the BIOS. Depending on the sophistication of the operating system, the user then could configure the offending cards manually (on-screen) or turn the system off and set switches on the physical cards. When the system is restarted, the system is checked for remaining (or new) conflicts, any of which are brought to the user’s attention. Through this repetitive process, all system conflicts are resolved.


Note:  
Plug and Play is still going through some revisions. Windows 95 requires at least version 1.0a of the ISA PnP BIOS. If your system does not have the most current BIOS, I suggest that you install a BIOS upgrade. With the Flash ROM used in most PnP systems, you can just download the new BIOS image from the system vendor or manufacturer and run the supplied BIOS update program.


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