Host side cable detection, Figure 58. host-side ide cable detection, 1 host side cable detection – Intel 815 User Manual

Page 114: Bios detects cable type using gpios

I/O Subsystem

114

Intel

815 Chipset Platform Design Guide

10.2.1

Host Side Cable Detection

BIOS Detects Cable Type Using GPIOs

Host-side detection requires the use of two GPI pins (one per IDE controller). The proper way to
connect the PDIAG#/CBLID# signal of the IDE connector to the host is shown in Figure 58. All
Ultra ATA/66 devices have a 10 k

Ω

pull-up resistor to 5V. Most GPIO pins on the ICH and all

GPIs on the FWH are not 5V tolerant. This requires a resistor divider so that 5V will not be driven
to the ICH or FWH pins. The proper value of the series resistor is 15 k

Ω

(as shown in the

following figure). This creates a 10 k

Ω

/15 k

Ω

resistor divider and will produce approximately 3V

for a logic high. This mechanism allows the host to sample PDIAG#/CBLID#, after diagnostics. 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.

Figure 58. Host-Side IDE Cable Detection

80-conductor

IDE cable

IDE Drive

10 k

Ω

5 V

PDIAG

ICH

GPIO

To secondary

IDE connector

Open

15 k

Ω

40-conductor

cable