I/O Controller Hub 2
R
134 Intel
®
Pentium
®
4 Processor / Intel
®
850 Chipset Family Platform Design Guide
9.1.2 Cable Detection for Ultra ATA/66 and Ultra ATA/100
The ICH2 IDE Controller supports PIO, Multi-word (8237 style) DMA, and Ultra DMA modes 0
through 5. The ICH2 needs to determine the type of cable that is present, in order 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, ground, signal, ground, etc. 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 or ATA/100 mode can be enabled, the ICH2 requires the system software
to attempt to determine the cable type used in the system. If the system software detects an 80-
conductor cable, it may use any Ultra DMA mode up to the highest transfer mode supported by
both the chipset and the IDE device. If a 40-conductor cable is detected, the system software must
not enable modes faster than Ultra DMA Mode 2 (Ultra ATA/33).
Intel recommends that cable detection be done using a combination Host-Side/Device-Side
detection mechanism. Note that Host-Side detection cannot be implemented on an NLX form
factor system, since this configuration does not define interconnect pins for the PDIAG#/CBLID#
from the riser (containing the ATA connectors) to the motherboard. These systems must rely on
the Device-Side Detection mechanism only.
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