ML2653CH View Datasheet(PDF) - Micro Linear Corporation
Part Name
Description
MFG CO.
'ML2653CH' PDF : 23 Pages View PDF
FUNCTIONAL DESCRIPTION (Continued)
2–7ms apart in the link fail state, the device ignores the link
pulses and resets the number of consecutive link pulses to
zero. After the link pulse fail state is exited, transmission and
reception can be resumed.
Link pulse status is indicated by the LTP pin. LTP is a dual
function input/output pin that acts both as an active low link
test pass output and a link test disable input. The pin consists
of an open drain output with an internal pull-up resistor. If
the pin is tied to GND, the pin acts as an input and the link
test function is disabled. If the pin is not tied to GND, the pin
acts as an active low link test pass output and can drive an
LED from VCC or another digital output. Thus, the LED is lit
when the link test is passing.
JABBER
The transmit section contains a jabber detect circuit.
Jabber is a fault condition characterized by a babbling
transmitter. The ML2652 and ML2653 detect jabber when
a transmission packet exceeds 20–150ms in length. If
jabber detect occurs, the transmit output is disabled, the
collision signal COL is sent over the controller interface,
and the JAB pin is pulled low. The device remains in the
jabber detect state until there is at least 250–750ms of
continuous non-transmission. Note that link pulses
continue to be transmitted even when the device is in the
jabber condition.
The jabber detection circuitry can be disabled (only on the
ML2652) with the JABDIS pin for testing and diagnostic
purposes. Disabling jabber means that a jabber condition
is never recognized, even when it occurs. JABDIS is an
active high jabber disable input and has an internal pull-
down resistor to GND.
COLLISION
Collision occurs whenever the DTE card is transmitting
and receiving data simultaneously. However, the collision
circuit on the ML2652 operates differently depending on
whether twisted pair interface or AUI is being used.
When the twisted pair interface is used, collision occurs
whenever the device is transmitting and receiving data
simultaneously, that is when both RxE and TxE are active.
The collision state is indicated by COL and CLS pins. COL
is used to signal collision to the controller. CLS is an active
low open drain output. CLS is activated during Jabber, but
not during SQE test while COL is activated during both.
When the AUI is used (ML2652 only), collision is no
longer detected from simultaneous transmission and
reception, but the collision state is determined when a
collision signal is present on the AUI collision inputs, CI+
and CI–. A 10 MHz square wave has to be applied to this
input in order for the device to signal the collision state on
COL and CLS.
The CLS pin is an output that indicates collision activity.
The pin consists of an open drain output with an internal
ML2652/ML2653
pull-up resistor and can drive an LED from VCC or another
digital input. In order to make an LED visible, CLS has an
internal blinker circuit that generates a 100ms blink (50ms
high, 50ms low) that is triggered when a collision starts. At
the completion of the 100ms blink period, if collision is in
progress, another 100ms blink is generated.
SQE TEST
When the twisted pair interface is used, the device tests
the collision circuitry at the end of each transmission by
sending a 1µs collision pulse over the COL pin. This is
known as SQE (signal quality error) test and is shown in
the transmit timing diagram in Figure 1. The SQE test is
disabled if the device is in jabber detect state or link pulse
fail condition.
When AUI is used (ML2652), the SQE test pulse is
generated by an external MAU and the external MAU
sends the SQE test pulse to the ML2652 via the collision
inputs , CI+ and CI–. The ML2652 then relays the collision
signal to the controller via the COL and CLS output pins.
RECEIVE POLARITY DETECT AND AUTO CORRECTION
The ML2652 and ML2653 contain an auto-polarity circuit
that detects the polarity of the receive twisted pair leads,
Rx+ and RX-and internally reverses the leads if their
polarity is incorrect.
When the device is powered up, it is assumed that the
polarity is correct and no polarity correction occurs. Then
receive polarity is continuously monitored by checking the
polarity of the SOI and link pulses since they are always
positive pulses. If either 2 consecutive SOI or 4
consecutive link pulses have incorrect RX± polarity, then
the auto-polarity circuit internally reverses the Rx+ and
Rx– connections.
AUI (APPLIES ONLY TO ML2652)
The ML2652 can be used with an external MAU via the
Attachment Unit Interface (AUI). When the AUI is used,
the internal MAU functions and twisted pair interface are
disabled, and the device only uses the manchester
encoder and decoder functions, as shown in the block
diagram. The AUI consists of three differential signal pairs:
DI, DO, and CI. The function of each pair is described
below.
The DO+ and DO– are differential outputs to the external
MAU which contain the transmit data output from the
Manchester encoder. The DO+ and DO– output drivers
are capable of driving 50 meters of 78 ohm cable with less
than 5ns rise and fall time and less than ±0.5ns of jitter. In
addition, at the end of transmission, the AUI output driver
inserts a 200ns minimum pulse and meets the turnoff and
idle characteristics specified in IEEE 802.3–1988. An
external 78 ohm resistor across DO+ and DO– is required
as shown in Figure 12 to develop the proper output levels
from the internal current sources. The DO+ and DO–
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