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ML4644CQ

4 Port AUI Multiplexer

Micro Linear Corporation 

FUNCTIONAL DESCRIPTION

Figure 1 is a block diagram of a Four Port Multiplexer

using the ML4644. All AUI interfaces are transformer

coupled as required in an AUI connection.

RECEPTION

The receive function consists of detecting data on receive

differential data input pair of the MAU port (RxIN) and

transmitting this data out of the RxOUT ports of all the DTE

port. This data will only be passed onto the DTE port if it

meets the unsquelch criteria of the AUI receiver circuit. This

provision prevents any noise on the AUI cable from being

misinterpreted as data and transmitted to the RxOUT pins.

The receiver squelch circuit rejects signal typically with

pulse width less than 20ns or a voltage level more positive

than –250mV. Once the receiver is unsquelched, it

remains so until reception of the idle signal which is more

positive than –170mV for longer than 180ns.

TRANSMISSION

The transmit function consists of detecting data on any of

the four differential data input pairs (TxIN1, TxIN2, TxIN3,

and TxIN4) and transmitting this data out of the TxOUT

pair of the MAU port.

Only data that meets the unsquelch criteria of the AUI

receiver circuit will be passed onto the TxOUT port.

LOOPBACK

If the ML4644 is connected to a MAU, or connected to

other 4642/44s that are connected to a MAU, the MAU

should be used to provide loopback. The loopback function

of the MAU will loop data back to the RxIN port which will

pass is to all FxOUTs and the REC pin will go low. In some

configurations, there will be no MAU, and a ML4644 will

be the last chip in the Tx path. In this case, the RxIN port

will never be active, since it is not connected, and the REC

pin has no function. The REC pin may be grounded and this

will put the ML4644 in loopback mode, and data on the

TxIN pair will be looped back to all RxOUT ports.

COLLISION

There are two possible collision scenarios.

1. Collision from the network connected to the MAU.

2. Collision between two or more DTEs attached to the

multiplexer.

In the case of a network collision, the MAU will send a

collision presence signal to the multiplexer. The ML4644

will propagate this signal to the CDOUT pins of each of the

DTE ports. The collision signal is a 10MHz ±0.01% signal.

When a collision event occurs between two or more DTE

ports, the ML4644 will send the collision presence signal to

each of the DTEs via the collision ports. At the same time a

5MHz JAM signal is sent to the network.

ML4644

SQE TEST FUNCTION

The Signal Quality Error (SQE) test function allows the

DTE to determine whether or not the collision port is

functional. After each transmission, during the interpacket

gap time, the collision signal will be activated on the

CDOUT port of the same DTE port data has been

transmitted, for typically 1µs. The SQE function is not

activated at the DTE ports that are in jabber state. The SQE

function of each port can be disabled by tying the SQEN

pin high.

JABBER FUNCTION

The jabber function prevents a malfunction transmitter

from continuous transmission and thus loaded down the

network. Within the ML4644, there is a jabber timer. The

timer starts at the beginning of a received packet and

resets at the end of each packet. If the packet lasts longer

than 7 to 20ms the jabber circuit will disable the

offending TxIN receiver (the transmission of excessively

long packet is thus terminated) and generates a collision

signal to the collision port of the offending DTE port. The

DTE port will exit the jabber state when the transmission

goes idle.

LED DRIVERS

The ML4644 has ten LED drivers. Each DTE port has a

transmit LED and a jabber LED and the MAU port has a

receive LED. Additionally there is a collision LED which

indicates the presence of a collision condition. All LED

drivers are active low open collector driver.

All LED drivers except the jabber have pulse 1ms pulse

stretchers. The pulse stretchers provide adequate on time

for the LED to be visible.

CASCADING THE ML4644 FOR EIGHT PORT

MULTIPLEXER APPLICATION

An 8 port multiplexer can be realized by using two

ML4644s and one ML4642. In this configuration (see fig.

2), the SQE function of the ML4642 should be disabled to

prevent false collision signalling. The SQE function in this

configuration is performed by each DTE port of the

ML4644 independently. Only one crystal is required,

since X3 of the ML4644 with the crystal can drive X1 of

the other chip.

ML4644

ML4644

ML4642

Figure 2. Block Diagram of an Eight port Multiplexer.

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