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Technical Reference

2.5 DMA Channels

Table 13. DMA Channels

DMA Channel Number Data Width System Resource

0 8 or 16 bits Open

1 8 or 16 bits Parallel port

2 8 or 16 bits Diskette drive

3 8 or 16 bits Parallel port (for ECP or EPP)

4 8 or 16 bits DMA controller

5 16 bits Open

6 16 bits Open

7 16 bits Open

2.6 PCI Conventional Interrupt Routing Map

This section describes interrupt sharing and how the interrupt signals are connected between the

PCI Conventional bus connectors and onboard PCI Conventional devices. The PCI Conventional

specification describes how interrupts can be shared between devices attached to the PCI

Conventional bus. In most cases, the small amount of latency added by interrupt sharing does not

affect the operation or throughput of the devices. In some special cases where maximum

performance is needed from a device, a PCI Conventional device should not share an interrupt with

other PCI Conventional devices. Use the following information to avoid sharing an interrupt with a

PCI Conventional add-in card.

PCI Conventional devices are categorized as follows to specify their interrupt grouping:

• INTA: By default, all add-in cards that require only one interrupt are in this category. For

almost all cards that require more than one interrupt, the first interrupt on the card is also

classified as INTA.

• INTB: Generally, the second interrupt on add-in cards that require two or more interrupts is

classified as INTB. (This is not an absolute requirement.)

• INTC and INTD: Generally, a third interrupt on add-in cards is classified as INTC and a fourth

interrupt is classified as INTD.

The ICH7 has eight Programmable Interrupt Request (PIRQ) input signals. All PCI Conventional

interrupt sources either onboard or from a PCI Conventional add-in card connect to one of these

PIRQ signals. Some PCI Conventional interrupt sources are electrically tied together on the board

and therefore share the same interrupt. Table 14 shows an example of how the PIRQ signals are

routed.

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