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參數(shù)資料
| 型號(hào)： | AM79C974 |
| 廠商： | Advanced Micro Devices, Inc. |
| 英文描述： | PCnetTM-SCSI Combination Ethernet and SCSI Controller for PCI Systems |
| 中文描述： | PCnetTM -的SCSI結(jié)合以太網(wǎng)和SCSI控制器PCI系統(tǒng) |
| 文件頁(yè)數(shù)： | 126/153頁(yè) |
| 文件大?。?/td> | 838K |
| 代理商： | AM79C974 |
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AMD
P R E L I M I N A R Y
126
Am79C974
18681A-66
This is optional. Use
accordingly to terminate both
ends of the SCSI Bus.
CPU
Memory
Internal
Drive
(Terminated)
Riser Card
High-Density
SCSI-2
Termination
External SCSI
Bus Cable
External
Peripheral
High-Density
SCSI-2
Connectors
Keyboard
Connector
To SCSI CLK1
and CLK2
Am79C974
To DC Power
Ferrite Bead
to PCI Bus
T
25
Mounted
High-Density
SCSI-2
Connector
T
Figure E-4. Motherboard Layout — Approach #2
Motherboard designs which place an internal and exter-
nal connector on either side of the Am79C974 are dis-
couraged since:
Two SCSI connectors are required on the mothe-
rboard—one more than what the other two ap-
proaches call for.
When the number of internal and external bus
components increase, the on-board terminators
would have to be turned off either through software
or hardware, which may be undesirable to a board
designer.
The possibility for creating stubs exists if the con-
nectors and Am79C974 are not routed correctly.
See Figure E-1 for the ideal routing scheme.
NOISE CONSIDERATIONS
Some areas of a PCI motherboard or host adapter de-
sign (which include the Am79C974) are more suscepti-
ble to noise. They are:
the 40 MHz crystal oscillator
the SCSI cables
the DC power planes
pins on the ICs, specifically the Am79C974.
Electromagnetic Interference (EMI)
There are several ways to reduce the amount of noise
present in these areas:
A 40 MHz crystal oscillator must be used in order
to have a 10 MB/s SCSI data rate. Use of this
40MHz crystal oscillator, which drives the
SCSICLK pin on the Am79C974, introduces the
possibility of unwanted high frequency compo-
nents, including harmonics, coupling with
Am79C974 signals. To help prevent this, a resistor
should be placed in series with the oscillator to
form a low pass filter with the input capacitance
(10 pF) of the SCSI CLK pin. This filter reduces the
edge rate of the clock waveform, increasing both
rise and fall times by 2ns. This removes higher
frequencies, specifically harmonics from the crystal
oscillator waveform and thus reduces the amount
of noise introduced into the Am79C974.
A ferrite bead, which is essentially an inductor,
may be used with the oscillator to prevent coupling
of higher frequencies with DC power supply sig-
nals. The ferrite bead blocks high frequency noise
while acting like a short to the DC components.
相關(guān)PDF資料 |
PDF描述 |
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| AM79C974KCW | PCnetTM-SCSI Combination Ethernet and SCSI Controller for PCI Systems |
| AM79C975 | PCnet⑩-FAST III Single-Chip 10/100 Mbps PCI Ethernet Controller with Integrated PHY |
| AM79C973 | PCnet⑩-FAST III Single-Chip 10/100 Mbps PCI Ethernet Controller with Integrated PHY |
| AM79C973KCW | PCnet⑩-FAST III Single-Chip 10/100 Mbps PCI Ethernet Controller with Integrated PHY |
| AM79C975KCW | PCnet⑩-FAST III Single-Chip 10/100 Mbps PCI Ethernet Controller with Integrated PHY |
相關(guān)代理商/技術(shù)參數(shù) |
參數(shù)描述 |
|---|---|
| AM79C974KC | 制造商:Advanced Micro Devices 功能描述: |
| AM79C974KC/W | 制造商:未知廠家 制造商全稱:未知廠家 功能描述:LAN Node Controller |
| AM79C974KCW | 制造商:AMD 制造商全稱:Advanced Micro Devices 功能描述:PCnetTM-SCSI Combination Ethernet and SCSI Controller for PCI Systems |
| AM79C975 | 制造商:AMD 制造商全稱:Advanced Micro Devices 功能描述:PCnet⑩-FAST III Single-Chip 10/100 Mbps PCI Ethernet Controller with Integrated PHY |
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