am79c974 Advanced Micro Devices, am79c974 Datasheet - Page 127

• Manufacturer Part Number: am79c974
• Description: Pcnettm-scsi Combination Ethernet And Scsi Controller For Pci Systems
• Manufacturer: Advanced Micro Devices

Decoupling Methods
As stated in Appendix C, decoupling capacitors should
be used across the VDD and VSS pins on the motherboard
There are pairs of VDD and VSS pins on the Am79C974
that should each have their own decoupling capacitor.
The following decoupling method should be used for the
VDD/VSS pairs:
From an EMI standpoint, SCSI-2 high-density ca-
bles should be used instead of a SCSI-1 cables.
Unlike the SCSI-1 flat ribbon cable, the SCSI-2
cable is electrically more substantial. It is shielded
and signal wires are strategically placed for better
signal travel.
P R E L I M I N A R Y
Am79C974
Connect the capacitor directly between a VDD/VSS
pair of the Am79C974 so that it sits on the compo-
nent side of the board. This configuration will allow
the capacitor to filter undesired high frequency
components directly at the Am79C974 and not
only at the power planes. This not only minimizes
the noise on the power planes that the chip sees,
but it also filters any noise generated by the chip
before it reaches the power planes. The leads to
each end of the capacitor should be wide and may
contain several feed-throughs to the VDD and VSS
planes to reduce the inductance present. Refer to
Figure E-5.
AMD
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