Ultra Ata/66; Ultra Ata/66 Detection - Intel VC820 - Desktop Board Motherboard Design Manual

Layout/Routing Guidelines
2.13

Ultra ATA/66

This section contains guidelines for connecting and routing the ICH IDE interface. The ICH 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 ICH has integrated the 33
the IDE data signals running to the two ATA connectors.
The IDE interface can be routed with 5 mil traces on 5 mil spaces, and must be less than 8 inches
long (from ICH to IDE connector). Additionally, the shortest IDE signal (on a given IDE channel)
must be less than 0.5" shorter than the longest IDE signal (on that channel).
Cable
•
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 next closest connector to the end of the cable (6" away
from the end of the cable).
•
Grounding: Provide a direct low impedance chassis path between the motherboard ground
and hard disk drives.
•
ICH Placement: The ICH must be placed equal to or less than 8 inches from the ATA
connector(s).
•
PC99 requirement: Support Cable Select for master-slave configuration is a system design
requirement for Microsoft* PC99. CSEL signal needs to be pulled down at the host side by
using a 470
2.13.1

Ultra ATA/66 Detection

®
The Intel
chipset needs to determine the installed IDE device mode and the type of cable to configure its own
hardware and software to support it.
A new IDE cable is required for Ultra ATA/66. This cable is an 80 conductor cable; however the 40
pin connectors do not change. The wires in the cable alternate: ground, signal, ground, signal,
ground, signal, ground... All the 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 to the Small Form Factor Specification SFF-8049. This specification can be obtained
from the Small Form Factor Committee.
To determine if ATA/66 mode can be enabled, the Intel
attempt to determine the cable type used in the system. The BIOS does this in one of two ways:
•
Host Side Detection
•
Device Side Detection
If the BIOS detects an 80-conductor cable, it may use any Ultra DMA mode up to the highest
transfer mode supported by both the Intel
can only enable modes that do not require an 80-conductor cable (e.g., Ultra ATA/33 Mode).
After determining the Ultra DMA mode to be used, the BIOS will configure the Intel
hardware and software to match the selected mode.
2-56
Ω
pull-down resistor for each ATA connector.
820 chipset supports many Ultra DMA modes including ATA/66. The Intel
Ω
series resistors that have been typically required on
®
820 chipset requires the system BIOS to
®
820 chipset and the IDE device. Otherwise, the BIOS
Intel
®
820
®
820 chipset
®
820 Chipset Design Guide