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參數(shù)資料
| 型號： | Am79C965A |
| 廠商： | Advanced Micro Devices, Inc. |
| 英文描述： | PCnet?-32 Single-Chip 32-Bit Ethernet Controller |
| 中文描述： | PCnet？-32單芯片32位以太網(wǎng)控制器 |
| 文件頁數(shù)： | 97/228頁 |
| 文件大小： | 1681K |
| 代理商： | AM79C965A |
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Am79C965A
97
will be set in the Transmit Descriptor Ring (TMD2,
bit27) after the frame has been transmitted.
Differential Input Terminations
The differential input for the Manchester data (DI±) is
externally terminated by two 40.2 W ±1% resistors and
one optional common-mode bypass capacitor, as
shown in the Differential Input Termination diagram be-
low. The differential input impedance, ZIDF, and the
common-mode input impedance, ZICM, are specified
so that the Ethernet specification for cable termination
impedance is met using standard 1% resistor
terminators. If SIP devices are used, 39 W is also a
suitable value. The CI± differential inputs are
terminated in exactly the same way as the DI± pair.
Figure 31. AUI Differential Input Termination
Collision Detection
A MAU detects the collision condition on the network
and generates a differential signal at the CI± inputs.
This collision signal passes through an input stage
which detects signal levels and pulse duration. When
the signal is detected by the MENDEC it sets the
ICLSN line HIGH. The condition continues for
approximately 1.5 bit times after the last LOW-to-HIGH
transition on CI±.
Twisted-Pair Transceiver (T-MAU)
The T-MAU implements the Medium Attachment Unit
(MAU) functions for the Twisted Pair Medium, as speci-
fied by the supplement to ISO 8802-3 (IEEE/ANSI
802.3) standard (Type 10BASE-T). The T-MAU pro-
vides twisted pair driver and receiver circuits, including
on-board transmit digital predistortion and receiver
squelch and a number of additional features including
Link Status indication, Automatic Twisted Pair Receive
Polarity Detection/Correction and Indication, Receive
Carrier Sense, Transmit Active and Collision Present
indication.
T-MAU gets reset during power-up by H_RESET, by
S_RESET when reset port is read, or by asserting the
RESET pin. T-MAU is not reset by STOP.
Twisted Pair Transmit Function
The differential driver circuitry in the TXD± and TXP±
pins provides the necessary electrical driving capability
and the pre-distortion control for transmitting signals
over maximum length Twisted Pair cable, as specified
by the 10BASE-T supplement to the ISO 8802-3 (IEEE/
ANSI 802.3) Standard. The transmit function for data
output meets the propagation delays and jitter
specified by the standard.
Twisted Pair Receive Function
The receiver complies with the receiver specifications
of the ISO 8802-3 (IEEE/ANSI 802.3) 10BASE-T Stan-
dard, including noise immunity and received signal re-
jection criteria (
‘
Smart Squelch
’
). Signals meeting this
criteria appearing at the RXD± differential input pair are
routed to the MENDEC. The receiver function meets
the propagation delays and jitter requirements
specified by the standard. The receiver squelch level
drops to half its threshold value after unsquelch to allow
reception of minimum amplitude signals and to offset
carrier fade in the event of worst case signal
attenuation and crosstalk noise conditions.
Note that the 10BASE-T Standard defines the receive
input amplitude at the external Media Dependent Inter-
face (MDI). Filter and transformer loss are not
specified. The T-MAU receiver squelch levels are
defined to account for a 1 dB insertion loss at 10 MHz,
which is typical for the type of receive filters/
transformers employed.
Normal 10BASE-T compatible receive thresholds are
employed when the LRT (CSR15[9]) bit is LOW. When
the LRT bit is set (HIGH), the Low Receive Threshold
option is invoked, and the sensitivity of the T-MAU re-
ceiver is increased. This allows longer line lengths to
be employed, exceeding the 100 m target distance of
normal 10BASE-T (assuming typical 24 AWG cable).
The increased receiver sensitivity compensates for the
increased signal attenuation caused by the additional
cable distance.
However, making the receiver more sensitive means
that it is also more susceptible to extraneous noise, pri-
marily caused by coupling from co-resident services
(crosstalk). For this reason, it is recommended that
when using the Low Receive Threshold option that the
service should be installed on 4-pair cable only. Multi-
pair cables within the same outer sheath have lower
crosstalk attenuation, and may allow noise emitted
from adjacent pairs to couple into the receive pair, and
be of sufficient amplitude to falsely unsquelch the
T-MAU.
DI+
DI-
40.2
40.2
0.01
μ
F
to 0.1
μ
F
AUI Isolation
Transformer
PCnet 32
18219-38
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相關(guān)代理商/技術(shù)參數(shù) |
參數(shù)描述 |
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| AM79C965AWW WAF | 制造商:Advanced Micro Devices 功能描述: |
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