Combination Host-Side/Device-Side Cable Detection; Figure 87. Combination Host-Side/Device-Side Ide Cable Detection - Intel Pentium 4 Design Manual

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9.1.2.1

Combination Host-Side/Device-Side Cable Detection

Host side detection (described in the ATA/ATAPI-4 Standard, Section 5.2.11) requires the use of
two GPI pins (one for each IDE channel). The proper way to connect the PDIAG#/CBLID# signal
of the IDE connector to the host is shown in Figure 87. All IDE devices have a 10 kΩ pull-up
resistor to 5 volts on this signal. Not all of the GPI and GPIO pins on the ICH2 are 5-volt tolerant.
If non 5-volt tolerant inputs are used, a resistor divider is required to prevent 5 volts on the ICH2
or FWH pins. The proper value of the divider resistor is 10 kΩ (as shown in Figure 87).

Figure 87. Combination Host-Side/Device-Side IDE Cable Detection

ICH2
Resistor required for
non 5V tolerant G PI
ICH2
Resistor required for
non 5V tolerant G PI
This mechanism allows the BIOS, after diagnostics, to sample PDIAG#/CBLID#. If the signal is
high then there is 40-conductor cable in the system and ATA modes 3, 4, and 5 must not be
enabled.
If PDIAG#/CBLID# is detected low, then there may be an 80-conductor cable in the system, or
there may be a 40-conductor cable and a legacy slave device (Device 1) that does not release the
PDIAG#/CBLID# signal as required by the ATA/ATAPI-4 standard. In this case, BIOS should
check the IDENTIFY DEVICE information in a connected device that supports Ultra DMA modes
higher than 2. If ID Word 93, bit 13 is a 1, then an 80-conductor cable is present. If this bit is 0,
then a legacy slave (Device 1) is preventing proper cable detection, and BIOS should configure the
system as though a 40-conductor cable is present, and notify the user of the problem.
® ®
Intel Pentium 4 Processor / Intel
To secondary
IDE connector
40-conductor
G PIO
cable
PDIAG#/
CBLID#
G PIO
10 k Ω
To secondary
IDE connector
80-conductor
G PIO
IDE cable
PDIAG#/
CBLID#
G PIO
10 k Ω
®
850 Chipset Family Platform Design Guide
IDE drive
5 V
10 k Ω
PDIAG #
IDE drive
5 V
10 k
Ω
PDIAG #
Open
I/O Controller Hub 2
IDE drive
5 V
10 k Ω
PDIAG #
IDE drive
5 V
10 k Ω
PDIAG#
IDE_combo_cable_det
135