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Dual channel master mode PCI supports four Enhanced IDE devices. The transfer rate for each device can support up 33 MB/sec
to cover PIO mode 4, multi-word DMA mode 2 drives, and UltraDMA-33 interface. Transmission line effects and signal crosstalk
emerge in the IDE related signals. To eliminate ringing and reflection caused by the transmission line effect, trace length and
impedance match must be taken into account. An example IDE layout is shown in Figure 2-59. Recommended layout rules for
both primary and second IDE ports are listed below:
•
The trace attribute of all primary IDE signals is in a minimum of 6 mils wide and 9 mils between two adjacent traces. The
recommended trace length is less than 6 inches.
•
All ATA signals in Figure 2-59 require series termination resistors. The series resistors (R
inch of the VT82C686A chip. The series resistors (R
•
Signal DD7 needs a 10K pull-down on the VT82C686A chip side of series termination
•
Signal DREQ needs a 5.6K pull-down on the connector side of the series termination
•
Signal IRQ14 (or IRQ15) needs a 10K pull-down or pull-up (preferred) on the connector side of the series termination
•
Signal IORDY# needs a 1K pull-up on the connector side of the series termination
•
Pin 28 of the IDE connectors should be tied to ground with a 470 ohm serial resistor.
•
It is recommended to layout the following signals to each IDE connector in equal length. They are signals DD[15..0],
IOR#, IOW#, and IORDY#.
VT82C686A
(South Bridge)
Note 1: 10K ohm resistor pull-down for DD7 only
Preliminary Revision 0.5, November 19, 1999
R
A
33 ohm
F04
RSTDRV
PDIOW#
PDIOR#
PDDACK#
PDCS1#
PDCS3#
PDA[2..0]
DD[15..0]
10K ohm
(note 1)
Trace length (L2) < 6"
L2
IRQ14
PIORDY#
PDDREQ
Figure 2-59. IDE Interfaces Layout Guidelines
Design Guide - VT82C694X Apollo Pro133 with VT82C686A
) should be placed within 1 inch of the primary IDE connector.
B
Trace length (L1) < 6"
L1
R
B
82 ohm
470 ohm
67
) should be placed within 1
A
Primary
IDE
Connector
1
IDERST#
23
IOW#
25
IOR#
29
DACK#
33
CS1#
38
CS3#
DA[2..0]
DD[15..0]
VCC
10K ohm
31
IRQ14
VCC
1K ohm
27
IORDY#
21
DREQ
5.6K ohm
28
SPSYNC:CSEL
Motherboard Design Guidelines
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