LXT908KCA4Q データシートの表示（PDF） - Intel

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LXT908KCA4Q

Universal 3.3V 10BASE-T and AUI Transceiver

Intel 

Universal 3.3V 10BASE-T and AUI Transceiver — LXT908

The LXT908 also provides three additional loopback functions. An external loopback mode, useful

for system-level testing, is controlled by pin 21 (LEDC). When LEDC is tied Low, the LXT908

disables the collision detection and internal loopback circuits, to allow external loopback or full-

duplex operation.

“Normal” twisted-pair loopback is controlled by pin 22 (LBK). When the twisted-pair port is

selected and LBK is High, twisted-pair loopback is “forced”, overriding collisions on the twisted-

pair circuit. When LBK is Low, normal loopback is in effect.

AUI loopback is also controlled by the LBK pin. When the AUI port is selected and LBK is High,

data transmitted by the back-end is internally looped back from the TXD pin through the

Manchester encoder/decoder to the RXD pin. When LBK is Low, no AUI loopback occurs.

2.1.8

Collision Detection Function

The collision detection function operates on the twisted-pair side of the interface. For standard

(half-duplex) 10BASE-T operation, a collision is defined as the simultaneous presence of valid

signals on both the TPI circuit and the TPO circuit. The LXT908 reports collisions to the back-end

via the COL pin. If the TPI circuit becomes active while there is activity on the TPO circuit, the

TPI data is passed to the back-end over the RXD circuit, disabling normal loopback. Figure 6 is a

state diagram of the LXT908 collision detection function. Refer to Test Specifications for collision

detection and COL/CI output timing.

Note: For full-duplex operation, the collision detection circuitry must be disabled.

Figure 6. Collision Detection Function

A Power On

DO=Active ∗

TPI=Idle ∗

XMIT=Enable

Idle

TPI=Active

Output

TPO=DO

DI=DO

Input

DI=TPI

DO=Active ∗

TPI=Active ∗

XMIT=Enable

DO=Active ∗

TPI=Active ∗

XMIT=Enable

Collision

A

DO=Idle +

XMIT=Disable

TPO=DO

DI=TPI

CI=SQE

DO=Active ∗

TPI=Idle

DO=Idle

A

TPI=Idle

Datasheet

15

Document #: 249049

Revision #: 002

Rev. Date: June 19, 2001

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