am79c974 Advanced Micro Devices, am79c974 Datasheet - Page 129

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

Decoupling methods which are NOT recommended
include:
connecting a capacitor only between the VDD and
VSS planes so that it sits on the component side of
the board. This doesn’t allow the capacitor to re-
duce noise directly at the chip, but it does allow for
a reduction of power plane noise and of board
components. (capacitors).
connecting a capacitor only between the VDD and
VSS planes so that it sits on the solder side of the
board. This configuration also doesn’t allow direct
decoupling at the chip. It does save board space,
but it requires an extra manufacturing step.
VIN
C1
10 f
Alum. or
4.7 f Tant.
15 V
Regulator
Dropout
Voltage
Low
V adj
VOUT
R1
121
1%
1/4W
R2
154
1%
1/4W
Figure E-6. Regulated Termination
P R E L I M I N A R Y
Am79C974
2.85 V
C2
150 f
Alum. or
22 µf Tant.
10 V
TERMINATION CONSIDERATIONS
The use of active or regulated termination for termina-
tors on the motherboard is recommended (see Figure
E-6), while external SCSI terminators can be used to
terminate other parts of the SCSI bus. Terminators must
match the impedance seen by a signal at the end of the
SCSI bus to the characteristic impedance of the SCSI
bus. This impedance is typically 84 +/– 12
vary greatly with PC board characteristics and cabling.
R3-20 are
110
C3
.1 f
Ceramic
25 V
1%
R3-11
R12
R13
R14
R15
R16
R17
R18
R19
R20
TERMPWR
DB (0-7,P)
ATN
BSY
ACK
RST
MSG
SEL
C/D
REQ
I/O
18681A-68
AMD
, but can
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