Intel 440GX manual IDE Routing Guidelines, Cabling, Motherboard, 8. IDE Series Termination

Design Checklist

3.7.2IDE Routing Guidelines

This section contains guidelines for connecting and routing the PIIX4E IDE interface. The PIIX4E 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 current recommendations use 33 ohm resistors on all the signals running to the two ATA connectors, while the remaining signals use resistors between 22 and 47 ohm resistors.

3.7.2.1Cabling

1.Length of cable: Each IDE cable must be equal to or less than 18 inches.

2.Capacitance: Less than 30 pF.

3.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” from the end of the cable).

4.Grounding: Provide a direct low impedance chassis path between the motherboard ground and hard disk drives.

3.7.2.2Motherboard

1.PIIX4E Placement: The PIIX4E should be placed as close as possible to the ATA connector(s).

2.Resistor Location: When the distance between the PIIX4E and the ATA connectors exceeds 4 inches, the series termination resistors should be placed within 1 inch of the PIIX4E. Designs that place the PIIX4E within 4 inches of the ATA connectors can place the series resistors anywhere along the trace.

3.PC97 requirement: Support Cable Select for master-slave configuration is a system design requirement for Microsoft* PC97. CSEL signal needs to be ground at host side by using a 470 ohm pull-down resistor for each ATA connector.

4.Capacitance: The capacitance of each pin of the IDE connector on the host should be below 25 pF when the cables are disconnected from the host.

5.Series Termination: The following resistor values are the current recommendations.

Table 3-8. IDE Series Termination

Signal	Resistor
PDD[15:0]	33 ohm
PDA[2:0]	33 ohm
PDIOR#	33 ohm
PDIOW#	33 ohm
PDDREQ	33 ohm
PDCS1#	33 ohm
PDCS3#	33 ohm
PDDACK#	33 ohm
IRQ14	22-47 ohm
RESET#	22-47 ohm

Signal	Resistor
SDD[15:0]	33 ohm
SDA[2:0]	33 ohm
SDIOR#	33 ohm
SDIOW#	33 ohm
SDDREQ	33 ohm
SDCS1#	33 ohm
SDCS3#	33 ohm
SDDACK#	33 ohm
IRQ15	22-47 ohm

Intel®440GX AGPset Design Guide 3-20