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參數(shù)資料
| 型號： | EM2H |
| 廠商： | LSI CORP |
| 元件分類： | 網絡接口 |
| 英文描述： | 10Base-2 Ethernet Transceiver Module with On Board Isolation Transformer & DC/DC Converter(10Base-2 以太網收發(fā)器模塊（帶絕緣變壓器和 DC/DC變換器）) |
| 中文描述： | DATACOM, ETHERNET TRANSCEIVER, DIP14 |
| 文件頁數(shù)： | 3/12頁 |
| 文件大?。?/td> | 124K |
| 代理商： | EM2H |
Ether Module - EM2H
10Base-2
3
MD400153/B
12
DM Disable module s an active ow signal (inter-
nal 10K
pullup) that may be utilized to turn off
the Ether module in the event an alternative
transceiver is used, or for power conservation
purposes.
Description of the Module Functions
The module has five main functions, as shown n the block
diagram. These are the Transmitter; the Collision Detec-
tor; the Jabber Timer; the Receiver; and the DC/DC
Converter. The on-board SEEQ 83C92C provides all
functions except DC/DC conversion and AUI signal isola-
tion.
The Transmitter
The Transmitter takes differential output signals from the
MCC, and outputs these signals at the correct evels to the
network.
The transmit signal is sent to the module via a balanced
differential pair (TX
±
). A squelch circuit prevents the
Transmitter Output from responding to noise on the TX
±
pair. The Transmitter has an open-collector current driver
output using the V
supply. Rise and fall times are
controlled and set at 25 ns/V to lessen the higher harmon-
ics. Drive current levels are set by a bandgap voltage
reference and a internal 1K resistor. An internal diode is
also added to reduce COAX loading and capacitance to
comply with the ISO and ANSI/IEEE specifications.
The transmit squelch circuit blocks signals with pulse
widths less than 15 nanoseconds, (negative-going), or
with evels of ess han –175 millivolts. The squelch circuits
turn the Transmitter off at the end of a packet if the signal
stays higher than –175 millivolts for more than 190 nanos-
econds. See Figure 3, the Transmitter Timing Diagram.
The TXO signal is disabled when not transmitting to
prevent noise on he network. If he COAX cable s shorted
or open, no transmitted data appears on the Receiver
input. This condition can be detected by the station
equipment by running a loopback test.
Collision Detection
The Collision detector monitors the COAX Center Con-
ductor and senses the voltage conditions created by a
collision, where the COAX shield s used as a reference. A
collision condition can be detected when two or more
stations are transmitting, whether or not the local Trans-
mitter is activated. This is called Receive Mode Collision
Detection.
The detector signals a collision by sending the 10 MHz
oscillator signal through the Collision Pair (CD
±
) to the
MCC. The HeartbeatTest s performed at the end of each
transmitted data packet to verify the operation of the
detector.
A collision causes a –2.0 volt average DC level on the
center conductor of the network cable. This level passes
through a 4-pole Bessel low-pass filter for averaging. The
resulting signal is measured by a voltage comparator
against the threshold voltage V
of about -1.5 volts. A
collision is indicated when the center conductor average
level is more negative than the CDS level by the threshold
V
. The line driver is enabled within 900 ns of the onset
of the collision, and the 10 MHz signal s sent to the station
equipment.
The Heartbeat Test is a short burst of the collision signal
generated immediately after the transmission of a packet.
This test enables the 10 MHz collision signal for about 1
Figure 3. Transmitter Timing
TX±
TX0
tTd
50%
VTSQ
tTON
tTf
tTST
VTSQ
tTOFF
50%
90%
10%
tTr
TRANSMIT
ENABLE
tTID
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