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Microsoft Windows Logo Program System and Device Requirements  —  148

user of the system how interrupt resources are allocated on the platform and which devices cannot avoid sharing interrupts. System designers may provide this documentation or information as they deem most appropriate for their product. Some possible mechanisms include:

Documenting slots according to the order in which cards should be inserted to prevent interrupt sharing for as long as possible

Providing information on interrupt routing and sharing via system setup programs

Some instances need additional clarification to fit within the context of this guideline. At the system designer’s discretion, PCI devices can share an interrupt line under the following conditions:

One system interrupt line can be shared by all PCI devices on an expansion card. In other words, PCI INTA# - INTD# may share the use of a single system interrupt directed to a given PCI expansion slot. This instance of line sharing applies to both expansion card designs based on PCI multifunction devices and to expansion card designs using PCI-to-PCI bridges.

Devices can share an interrupt in a design where a system-board set has multiple instances of a given PCI device performing a specific function.

For example, two embedded PCI SCSI controllers on a system board can share a single system interrupt line. A single line can be shared when the functions of the devices are very similar, such as a case where one embedded SCSI controller may be dedicated to “narrow” (8-bit wide) SCSI devices and the other is dedicated to “wide” (16-bit wide) SCSI devices.

On the other hand, an embedded SCSI controller may not share an interrupt with an embedded network adapter on a system board, because they perform two different functions within the system and could contend for the shared interrupt in ways that will reduce overall system performance.

B10.3.4.5 Connector and terminator requirements
B10. Differential devices support DIFFSENS as defined in SPI-4 standard (or later).

Differential devices support DIFFSENS as defined in SPI-4 standard (or later).

Without DIFFSENS, the differential bus drivers or a single-ended device will suffer fatal thermal damage if a single-ended device is put on a differential bus.

The specification for DIFFSENS is defined in Section 5.4.2 of the SPI-4 standard.

B10. Automatic termination circuit and SCSI terminators meet SPI-4 standard (or later).

Parallel SCSI add-on adapters and on-board controllers must use automatic termination that allows a user to add external devices without removing the server case. Terminators used in the SCSI host adapter must be regulated terminators, which are also known as active, SCSI-3 SPI-4, or Boulay terminators. SCSI termination built onto internal cables must meet the SCSI-3 specification.

B10. Terminator power is supplied to the SCSI bus with overcurrent protection.

The host adapter must supply terminator power (TERMPWR) to the SCSI bus for system-board implementations using PCI or another expansion bus. All terminators on the external SCSI bus must be powered from the TERMPWR lines in the SCSI bus.

In addition, the circuit that supplies TERMPWR must have overcurrent protection built into it.

Mobile PC Note This feature is not required for battery-powered systems that implement the SCSI host adapter as a PC Card device because of battery consumption issues.

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