參數(shù)資料
型號(hào)： AM79C100
廠商： Advanced Micro Devices, Inc.
英文描述： Twisted-Pair Ethernet Transceiver Plus (TPEX Plus)
中文描述： 雙絞線以太網(wǎng)收發(fā)器（TPEX加）
文件頁(yè)數(shù)： 7/24頁(yè)
文件大?。?/td> 208K
代理商： AM79C100
Am79C100
7
FUNCTIONAL DESCRIPTION
The Twisted-Pair Ethernet Transceiver Plus (TPEX
Plus) complies with the requirements specified by the
IEEE 802.3 standard for the attachment unit interface
(AUI) and the 10BASE-T standard for a twisted-pair
medium attachment unit (MAU). TPEX Plus also imple-
ments a number of features in addition to the IEEE
802.3 standard. An outline of the functions of the
Am79C100 is given below.
Attachment Unit Interface (DO
The AUI electrical and functional characteristics com-
ply with those specified within the IEEE 802.3 docu-
ments, Sections 7 and 14. The AUI pins can be wired
to an isolation transformer, for a remote MAU applica-
tion, or directly to another device (e.g., Am7992B serial
interface adapter), in the case of a local DTE applica-
tion. The end-of-packet SQE Test function (heartbeat)
can be disabled to allow the device to be employed in a
repeater application.
Twisted-Pair Transmit Function
Data transmission to the 10BASE-T medium occurs
when valid AUI signals appear on the DO
pair. This data stream is routed to the differential driver
circuitry in the TXD
±
and TXP
provides the necessary electrical driving capability and
the predistortion control for transmitting signals over
maximum length twisted-pair cable, as specified by the
IEEE 802.3 10BASE-T standard. During transmission,
data is looped back to the DI
cating normal operation. The transmit function for data
output and loopback operations meets the propagation
delays and jitter specified by the standard. During nor-
mal transmission, and providing that TPEX Plus is not
in a Link Fail or Jabber state, the XMT pin will be driven
LOW, and can be used to drive a status LED directly.
Twisted-Pair Receive Function
The receiver complies with the receiver specifications
of the IEEE 802.3 10BASE-T standard, including noise
immunity and received signal rejection criteria (“Smart
Squelch”). Signals meeting these criteria appearing at
the RXD
±
differential input pair are routed to the DI
outputs. The receiver function meets the propagation
delays and jitter requirements specified by the stan-
dard. The receiver squelch level drops to approximately
half its threshold value after unsquelch to allow recep-
tion of minimum amplitude signals and to mitigate car-
rier fade in the event of worst-case signal attenuation
and crosstalk noise conditions. During receive, the
RCV pin is driven LOW and can be used to drive a sta-
tus LED directly.
±
, DI
±
, CI
±
)
±
differential
±
pins. The driver circuitry
±
differential circuit, indi-
±
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 speci-
fied. The TPEX Plus 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 rec-
ommended (see also Table 1).
Normal 10BASE-T-compatible receive thresholds are
employed when the LRT pin is inactive (HIGH). When
the LRT pin is externally pulled LOW, the Low Receive
Threshold option is invoked, and the sensitivity of the
TPEX Plus receiver is increased. This allows longer
line lengths to be employed, exceeding the 100 m tar-
get distance of normal 10BASE-T (assuming typical 24
AWG cable). The additional cable distance contributes
directly to increased signal attenuation and reduced
signal amplitude at the TPEX Plus receiver. However,
from a system perspective, making the receiver more
sensitive means that it is also more susceptible to
extraneous noise, primarily caused by coupling from
co-resident services (crosstalk). For this reason, it is
recommended that when using the Low Receive
Threshold option, the service should be installed on
4-pair cable only. Multipair cables within the same outer
sheath have lower crosstalk attenuation, may allow
noise emitted from adjacent pairs to couple into the re-
ceive pair, and be of sufficient amplitude to falsely un-
squelch the TPEX Plus.
Link Test Function
The Link Test function is implemented as specified by
the 10BASE-T standard. During periods of transmit
pair inactivity, “l(fā)ink beat” pulses will be sent periodically
over the twisted-pair medium to allow constant monitor-
ing of medium integrity.
When the Link Test function is enabled, the absence of
link beat pulses and receive data on the RXD
cause the TPEX Plus to go into a Link Fail state. In the
Link Fail state, data transmission, data reception, data
loopback, and collision detection functions are disabled
and remain disabled until valid data or >5 consecutive
link pulses appear on the RXD
the LNKST pin is internally pulled HIGH. When the link
is identified as functional, the LNKST pin is driven
LOW, and is capable of directly driving a “Link OK”
LED. In order to interoperate with systems that do not
implement Link Test, this function can be disabled by
grounding the LNKST pin. With Link Test disabled, the
data driver, receiver, and loopback functions, as well as
collision detection, remain enabled irrespective of the
presence or absence of data or link pulses on the
RXD
±
pair.
Polarity Detection and Reversal
The TPEX Plus receive function includes the ability to
invert the polarity of the signals appearing at the RXD
pair if the polarity of the received signal is reversed
(such as in the case of a wiring error). This feature al-
lows data packets received from a reverse-wired RXD
input pair to be corrected in the TPEX Plus prior to
transfer to the DTE via the AUI interface (DI
±
pair will
±
pair. During Link Fail,
±
±
±
). The
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