Ultra Ata/66 Detection - Intel 810A3 Design Manual

4.8.2

Ultra ATA/66 Detection

The 82801AA ICH supports Ultra ATA/66 devices. The ATA/66 cable is an 80-conductor cable;
however the 40 pin connectors used on motherboards for 40-conductor cables do not change as a
result of this new cable. The wires in the cable alternate: ground, signal, ground, signal, ground,
signal, ground, etc. All the ground wires are tied together at the connectors 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
system BIOS to 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 ICH and the IDE device. Otherwise, the BIOS can only enable
modes that do not require an 80-conductor cable (example: Ultra ATA/33 Mode).
After determining the Ultra DMA mode to be used, the BIOS will configure the Intel
chipset hardware and software to match the selected mode.
4.8.2.1 Ultra ATA/66 Motherboard Guidelines
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The Intel
different motherboard layout.
Host-Side Detection—BIOS Detects Cable Type Using GPIOs
Host side detection requires the use of two GPI pins (1 per IDE controller). The proper way to
connect the PDIAG#/CBLID# signal of the IDE connector to the host is shown in
Ultra ATA/66 devices have a 10 KΩ pull-up resistor to 5 volts. Most of the GPIO pins on the ICH
and all GPIs on FWH Flash BIOS are not 5 volt tolerant. This requires a resistor divider so that 5
volts will not be driven to the ICH or FWH Flash BIOS pins. The proper value of the series resistor
is 15 KΩ (as shown on
approximately 3 volts for a logic high.
This mechanism allows the host, after diagnostics, to sample PDIAG#/CBLID#. If PDIAG#/
CBLIB# is high, then there is 40-conductor cable in the system and ATA modes 3 and 4 should not
be enabled. If PDIAG#/CBLID# is low, then there is an 80-conductor cable in the system.
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Intel 810A3 Chipset Design Guide
810A3 chipset can use two methods to detect the cable type. Each mode requires a
Figure 4-19). This creates a 10 KΩ/15 KΩ resistor divider and will produce
Layout and Routing Guidelines
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810A3 chipset using the ICH requires the
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810A3
Figure 4-19. All
4-15