Автор: InferNO
Дата сообщения: 28.04.2002 17:40
Вот из TXT-шки скопировал:
Ethernet на 300 метров
Суть изменения состоит в отпайке выв. 16 от платы и пpипайке
от выв. 16 до выв. 10 r1 и от выв.16 до выв. 13 r2 :
--+ 10
|-------------*------+
| | |
| 14 | *
D |--------+----(-----(o) coax
P | 15 | |
8 |---|<---+ |
3 | П r1
9 | 16 |
2 |-------------+
| |
| П r2
| 13 |
|-------------+
|
--+
r1 - 150 r2 - 20k
В 3Сомах ставят 16R2 и 1к
В китайских каpтах r1 pавен 0 (пеpемычка), а r2 отсутствует
Кстати, не только 3сом-ы гаpантиpуют 300 м. Вот лежит SMC, та же каpтина,
pезистоpы пpавда 1к3 и 10к
В этом и состоит секpет 300м.
Источник - an-621.pdf фиpмы National
=== Cut ===
Designing the DP8392 for
Longer Cable Applications
The IEEE 802.3 standard is designed for 500 meters of
Ethernet cable and 185 meters of Cheapernet (RG58A/U)
cable. To extend such segments to 1000 meters of Ethernet
cable and 300 meters of Cheapernet cable requires utiliza-
tion of Transmit mode collision detection. This method is
described below.
COLLISION DETECTION SCHEMES
The collision circuitry monitors the coaxial DC level. If the
level is more negative than the collision threshold, the colli-
sion output is enabled.
There are two different collision detection schemes that can
be implemented with the CTI; Receive mode, and Transmit
mode. The IEEE 802.3 standard allows the use of receive
and transmit modes for non-repeater node applications. Re-
peaters are required to have to receive mode implementa-
tion. These different modes are defined as follows:
Receive Mode: Detects a collision between any two sta-
tions on the network with certainty at all times.
Transmit Mode: Detects a collision with certainty only
when the station is transmitting.
Table I summarizes the receive and transmit mode defini-
Receive Mode: The Receive mode scheme has a very sim-
ple truth table. However, the tight threshold limits make the
design of it difficult. The threshold in this case has to be
between the maximum DC level of one station (-1300 mV)
and the minimum DC level of two far stations (-1581 mV).
Several factors such as the termination resistor variation,
signal skew, and input bias current of non-transmitting
nodes contribute to this tight margin. On top of the
-1300 mV minimum level, the impulse response of the in-
ternal low pass filter has to be added. The CTI incorporates
a 4-pole Bessel filter in combination with a trimmed on
board bandgap reference to provide this mode of collision
detection.
Transmit Mode: In this case, collision has to be detected
only when the station is transmitting. Thus, collision caused
by two other nodes may or may not be detected. This fea-
ture relaxes the upper limit of the threshold. As a result of
this, longer cable segments can be used. With the CTI, a
resistor divider can be used at the Collision Detection Sense
(CDS) pin to lower the threshold from receive to transmit
mode.
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