O Subsystem; Ide Interface; Cabling; Cable Detection For Ultra Ata/66 And Ultra Ata/100 - Intel 815EG Design Manual

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11 I/O Subsystem
This chapter provides guidelines for connecting and routing the IDE, AC '97, USB, IO-APIC,
SMBus, PCI, LPC/FWH, and RTC subsystems.
11.1

IDE Interface

This section contains guidelines for connecting and routing the ICH2 IDE interface. The ICH2 has
two independent IDE channels. This section provides guidelines for IDE connector cabling and
motherboard design, including component and resistor placement and signal termination for both
IDE channels. The ICH2 has integrated the series resistors that typically have been required on the
IDE data signals (PDD[15:0] and SDD[15:0]) running to the two ATA connectors. Intel does not
anticipate requiring additional series termination, but OEMs should verify the motherboard signal
integrity via simulation. Additional external 0 Ω resistors can be incorporated into the design to
address possible noise issues on the motherboard. The additional resistor layout increases
flexibility by providing future stuffing options.
The IDE interface can be routed with 5 mil traces on 7 mil spaces and must be less than 8 inches
long (from ICH2 to IDE connector). Additionally, the shortest IDE signal (on a given IDE
channel) must be less than 0.5 inch shorter than the longest IDE signal (on that channel).
11.1.1

Cabling

• Length of cable: Each IDE cable must be equal to or less than 18 inches.
• Capacitance: Less than 30 pF
• Placement: A maximum of 6 inches between drive connectors on the cable. If a single drive
is placed on the cable it should be placed at the end of the cable. If a second drive is placed on
the same cable it should be placed on the connector next closest to the end of the cable
(6 inches away from the end of the cable).
• Grounding: Provide a direct, low-impedance chassis path between the motherboard ground
and hard disk drives.
• ICH2 Placement: The ICH2 must be placed at most 8 inches from the ATA connector(s).
11.2

Cable Detection for Ultra ATA/66 and Ultra ATA/100

The ICH2 IDE controller supports PIO, multiword (8237-style) DMA, and Ultra DMA modes 0
through 5. The ICH2 must determine the type of cable present, to configure itself for the fastest
possible transfer mode that the hardware can support.
An 80-conductor IDE cable is required for Ultra ATA/66 and Ultra ATA/100. This cable uses the
same 40-pin connector as the old 40-pin IDE cable. The wires in the cable alternate: ground,
signal, ground, signal' etc. All ground wires are tied together on the cable (and they are tied to the
ground on the motherboard through the ground pins in the 40-pin connector). This cable conforms
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Intel 815EG Chipset Platform Design Guide
I/O Subsystem
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