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参数资料
| 型号： | AM79C965KCW |
| 厂商： | ADVANCED MICRO DEVICES INC |
| 元件分类： | 微控制器/微处理器 |
| 英文描述： | 3 CHANNEL(S), LOCAL AREA NETWORK CONTROLLER, PQFP16 |
| 封装： | PLASTIC, QFP-160 |
| 文件页数： | 218/220页 |
| 文件大小： | 1197K |
| 代理商： | AM79C965KCW |
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P R E L I M I N A R Y
AMD
97
Am79C965
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 ac-
count 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 nor-
mal 10BASE-T (assuming typical 24 AWG cable). The
increased receiver sensitivity compensates for the in-
creased signal attenuation caused by the additional ca-
ble 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.
Link Test Function
The link test function is implemented as specified by
10BASE-T standard. During periods of transmit pair in-
activity, ’Link beat pulses’ will be periodically sent over
the twisted pair medium to constantly monitor medium
integrity.
When the link test function is enabled (DLNKTST bit in
CSR15 is cleared), the absence of link beat pulses and
receive data on the RXD
± pair will cause the T-MAU to
go into a link fail state. In the link fail state, data transmis-
sion, data reception, data loopback and the collision de-
tection functions are disabled, and remain disabled until
valid data or >5 consecutive link pulses appear on the
RXD
± pair. During link fail, the Link Status signal is inac-
tive. When the link is identified as functional, the Link
Status signal is asserted. The
LNKST pin displays the
Link Status signal by default.
Transmission attempts during Link Fail state will pro-
duce no network activity and will produce LCAR and
CERR error indications.
In order to inter-operate with systems which do not im-
plement Link Test, this function can be disabled by set-
ting the DLNKTST bit in CSR15. With link test disabled,
the data driver, receiver and loopback functions as well
as collision detection remain enabled irespective of the
presence or absence of data or link pulses on the RXD
±
pair. Link Test pulses continue to be sent regardless of
the state of the DLNKTST bit.
Polarity Detection and Reversal
The T-MAU 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 allows data
frames received from a reverse wired RXD
± input pair to
be corrected in the T-MAU prior to transfer to the
MENDEC. The polarity detection function is activated
following H_RESET or Link Fail, and will reverse the
receive polarity based on both the polarity of any previ-
ous link beat pulses and the polarity of subsequent
frames with a valid End Transmit Delimiter (ETD).
When in the Link Fail state, the T-MAU will recognize
link beat pulses of either positive or negative polarity.
Exit from the Link Fail state is made due to the reception
of 5–6 consecutive link beat pulses of identical polarity.
On entry to the Link Pass state, the polarity of the last 5
link beat pulses is used to determine the initial receive
polarity configuration and the receiver is reconfigured to
subsequently recognize only link beat pulses of the pre-
viously recognized polarity.
Positive link beat pulses are defined as received signal
with a positive amplitude greater than 585 mV (LRT =
HIGH) with a pulse width of 60 ns–200 ns. This positive
excursion may be followed by a negative excursion.
This definition is consistent with the expected received
signal at a correctly wired receiver, when a link beat
pulse which fits the template of Figure 14-12 of the
10BASE-T Standard is generated at a transmitter and
passed through 100 m of twisted pair cable.
Negative link beat pulses are defined as received sig-
nals with a negative amplitude greater than 585 mV with
a pulse width of 60 ns–200 ns. This negative excursion
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