參數(shù)資料
型號(hào)： 8502
英文描述： 8502 Ethernet MII to AUI Interface Adapter manual 7/97
中文描述： 8502以太網(wǎng)MII接口適配器的投資者聯(lián)盟手冊(cè)7 / 97
文件頁(yè)數(shù)： 10/55頁(yè)
文件大?。?/td> 457K
代理商： 8502
8502
4-10
MD400157/D
3.5.2 Transmit Activity Indication
Activity can be programmed to appear on the PLED0 pin
by appropriately setting the programmable LED output
select bits in the MI serial port Configuration register.
When the PLED0 pin is programmed to be an activity
detect output, this pin s asserted ow for 50 mS every time
a transmit or receive packet occurs. The PLED0 output is
open drain with resistor pullup and can drive an LED from
VCC or can drive another digital input.
XMT_LED is transmit activity output during normal opera-
tion. This pin is asserted high for 50 mS every time a
transmit packet occurs. The XMT_LED output can drive
an LED to GND or can drive another digital input.
3.5.3 Transmit Disable
The AUI ransmitter can be disabled by setting he ransmit
disable bit in the MI serial port Configuration register.
When the transmit disable bit is set, the AUI transmitter is
forced into the idle state, and no data is transmitted
regardless of the state of TX_EN.
3.5.4 Transmit Powerdown
The AUI transmitter can be powered down by setting the
transmit powerdown bit in the MI serial port Configuration
register. When the transmit powerdown bit is set, the AUI
transmitter is powered down, the AUI transmit output is
high impedance, and the rest of the device operates
normally.
3.6 AUI RECEIVER
3.6.1 Receiver
The AUI (Attachement Unit Interface) receiver converts
AUI levels to internal digital levels. There are two AUI
receivers on the 8502, one for data (DI
±
) and one for
collision (CI
±
).
The AUI inputs on the DI
±
pins are internally biased to
about 3V by internal 10K bias resistors. The AUI inputs
first pass through a low pass filter designed to eliminate
high frequency noise on the input. The output of the
receive filter then goes to two different types of compara-
tors, threshold and zero crossing. The threshold compara-
tor determines whether the signal is valid, and the zero
crossing comparator is used to sense the actual data
transitions once the signal is determined to be valid data.
The output of the threshold comparator goes to the
squelch circuit; the output of the zero crossing comparator
is used for clock and data recovery.
The AUI inputs on the CI
±
pins are internally biased to
about 3V by internal 10K bias resistors. The AUI inputs
first pass through ow pass filter designed to eliminate high
frequency noise on the input. The output of the collision
receive filter then goes to a collision threshold comparator
which converts the CI
±
nputs to nternal digital evels. The
output of the collision threshold comparator then goes to
the collision detect circuit.
3.6.2 Squelch
The squelch block determines if the data from the thresh-
old comparators (and hence, AUI inputs) contains valid
data. The hreshold comparator compares he DI
±
and CI
±
inputs against a fixed negative threshold, called the AUI
squelch level. If the input voltage to the threshold com-
parator does not exceed he ixed negative hreshold evel,
the receiver is in the squelched state. If the input voltage
exceeds the negative squelch level for more than 20 nS,
the data is considered to be valid and the receiver now
enters nto he unsquelch state. In he unsquelch state, he
AUI receive threshold level is reduced by approximately
30% for noise immunity reasons and is called the
unsquelch evel. While n the unsquelch state, the receive
squelch circuit looks for SOI (Start Of Idle) pulse to locate
the end of he packet. When he SOI signal s detected, he
receive squelch is turned on again. The AUI receiver
meets he AUI receive requirements defined n EEE 802.3
Section 7.
3.6.3 Receive Activity Indication
Activity can be programmed to appear on the PLED0 pin
by appropriately setting the programmable LED output
select bits in the MI serial port Configuration register.
When the PLED0 pin is programmed to be an activity
detect output, this pin s asserted ow for 50 mS every time
a transmit or receive packet occurs. The PLED0 output is
open drain with resistor pullup and can drive an LED from
VCC or can drive another digital input.
RCV_LED is receive activity output during normal opera-
tion. This pin is asserted high for 50 mS every time a
receive packet occurs. The RCV_LED output can drive an
LED to GND or can drive another digital input.
相關(guān)PDF資料
PDF描述
8502 Ethernet MII(Media Independent Interface) to AUI(Attachment Unit Interface) Interface Adapter(以太網(wǎng)獨(dú)立于媒體接口與附屬單元接口適配器)
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