AM79C974 datasheet(127/153 Pages) AMD

127 / 153 page

AMD

P R E L I M I N A R Y

127

Am79C974

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.

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:

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.

AM79C974 Datasheet(PDF) 127 Page - Advanced Micro Devices