78Q2123 Ver la hoja de datos (PDF) - Unspecified

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78Q2123

MicroPHY™ 10/100BASE-TX Transceiver

Unspecified 

Automatic MDI/ MDI-X Configuration

The 78Q2123/78Q2133 implement the automatic

MDI/MDI-X configuration detailed in IEEE-802.3

2002. This function eliminates the need for cross

over cables when connecting to another device.

When auto-switching is enabled, the

78Q2123/78Q2133 will attempt to detect activity on

its given configuration. If no activity is seen for

60ms, the device will switch to the other

configuration depending on a random number

sequence. The initial seed of the random number

generator can be set via MR24.3:0. In addition, the

part includes an asynchronous MDIX reset that

varies from 1.29 seconds to 1.57 seconds to ensure

lock step will not occur between two devices.

The 78Q2123/78Q2133 will also allow for auto-

switching while the part is not in auto-negotiation

mode. The IEEE 802.3 specification will not work in

this case if the other device is in auto-negotiation

mode. The 78Q2123/78Q2133 default to auto MDIX

enabled with parallel detection. Register bits

MR24.6 and MR24.7 are both defaulted to 1. The

78Q2123/78Q2133 will resolve the proper

configuration within 5 seconds.

78Q2123/78Q2133 MicroPHY™

10/100BASE-TX Transceiver

Page: 6 of 42

© 2009 Teridian Semiconductor Corporation

Rev 1.5

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