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Advanced 10/100 Unmanaged Repeater — LXT9883/9863

Datasheet

Document #: 249115

Revision #: 003

Rev. Date: 08/07/01

4.3

Inter-Repeater Backplane Compatibility

The Inter-repeater Backplane (IRB) comprises two parts:

• Local—the backplane between cascaded devices on the same board.

• Stack—the backplane between multiple boards.

Each of these backplanes consists of both analog and digital signals.

4.3.1

Local Backplane—3.3V Only

The LXT98x3 local backplane operates at 3.3V only. LXT98x and LXT91x devices operate at 5V.

LXT98x3 devices are, therefore, not cascadable with LXT98x and LXT91x devices.

Note:

Do not mix LXT98x3 with either LXT98x or LXT91x devices on the local backplanes.

4.3.2

Stack Backplane—3.3V or 5V

The LXT98x3 stack backplanes can be configured to be either 3.3V or 5V. COMP_SEL (Pin 39), a

special input pin, selects between the two voltage modes, depending on whether 3.3V or 5V is

applied.

4.3.2.1

3.3V-Only Stacks

Apply 3.3V to COMP_SEL, IR100CFSBP, IR10CFSBP, and IR10COLBP for LXT98x3 backplane

operation

4.3.2.2

For 5V Backwards Stackability

Apply 5V to COMP_SEL, IR100CFSBP, IR10CFSBP, and IR10COLBP for LXT98x and LXT91x

backplane operation.

Note:

With either mode (3.3V or 5V), COMP_SEL draws less than 3 mA.

1. The external pull-up resistor values remain the same, regardless of 3.3V or 5V backplane

operation.

2. The recommended digital signal external buffer has been changed to 74LVT245 for the

LXT98x3.

4.3.2.3

3.3V and 5.0V Stacking Boards Cannot Be Mixed

4.3.2.3.1

3.3V Operation

Boards designed for 3.3V backplane operation should only be stacked with other 3.3V boards.

Existing LXT98x or LXT91x based designs cannot operate in 3.3V.

4.3.2.3.2

Incompatible Stacking Configurations

The following stacking configurations are incompatible:

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