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Replacing EXAR XR-T5684 with an LXT301Z Short-Haul Transceiver
Application Note
January 2001
Order Number: 249137-001
As of January 15, 2001, this document replaces the Level One document known as AN127.
Information in this document is provided in connection with Intel(R) products. No license, express or implied, by estoppel or otherwise, to any intellectual property rights is granted by this document. Except as provided in Intel's Terms and Conditions of Sale for such products, Intel assumes no liability whatsoever, and Intel disclaims any express or implied warranty, relating to sale and/or use of Intel products including liability or warranties relating to fitness for a particular purpose, merchantability, or infringement of any patent, copyright or other intellectual property right. Intel products are not intended for use in medical, life saving, or life sustaining applications. Intel may make changes to specifications and product descriptions at any time, without notice. Designers must not rely on the absence or characteristics of any features or instructions marked "reserved" or "undefined." Intel reserves these for future definition and shall have no responsibility whatsoever for conflicts or incompatibilities arising from future changes to them. The Replacing EXAR XR-T5684 with an LXT301Z Short-Haul Transceiver may contain design defects or errors known as errata which may cause the product to deviate from published specifications. Current characterized errata are available on request. Contact your local Intel sales office or your distributor to obtain the latest specifications and before placing your product order. Copies of documents which have an ordering number and are referenced in this document, or other Intel literature may be obtained by calling 1-800-548-4725 or by visiting Intel's website at http://www.intel.com. Copyright (c) Intel Corporation, 2001 *Third-party brands and names are the property of their respective owners.
Application Note
Replacing EXAR XR-T5684 with an LXT301Z Short-Haul Transceiver
Contents
1.0 General Description ......................................................................................................... 5 1.1 1.2 1.3 1.4 Description of Interface ......................................................................................... 5 Features ................................................................................................................ 5 1.2.1 Digital Interface ........................................................................................ 5 Analog Interface .................................................................................................... 6 Additional Advantages...........................................................................................6
Figures
1 2 Example of Similar Intel and Exar Circuits ............................................................ 6 CLKDS Logic......................................................................................................... 6
Tables
1 Differences in Function of Pins..............................................................................5
Application Note
3
Replacing EXAR XR-T5684 with an LXT301Z Short-Haul Transceiver
1.0
General Description
Intel's LXT301Z single LIU can easily replace EXAR's XR-T5684 short-haul transceiver. Depending on the design, this application note shows that only minor changes are needed in the conversion. In addition, the LXT301Z transceiver offers the designer performance advantages such as T1 and E1 operation, line rate reference clock, and minimum 13.6 dB receiver sensitivity
1.1
Description of Interface
Both EXAR's and Intel's transceivers come in 28 pin PLCC and DIP packages. They have a similar pinout with 22 pins and functions in common. Table 1 describes the differences between the two devices. It names the differing pins and functions for each transceiver:
Table 1.
Differences in Function of Pins
Pin 1-LCLK 5-MODE 9-PD 10-CLKDS 27-N/C 26-TEST T5684 Function 8X or 16X clock Synch RX data Divider Clock disable No connect Factory test mode LXT301Z Function MCLK-1X master clock Host control 1k pull-up to VCC n/c LLOOP, low = off RLOOP, low = off
1.2
1.2.1
Features
Digital Interface
Two digital signals have functions different enough to require further explanation: CLKDS and MODE. The possibilities that can occur with CLKDS in the T5684 are:
* If CLKDS is at a logic level low (off), cutting the trace to pin 10 will work with the LXT301Z.
This is shown in Figure 1.
* If CLKDS is at a logic level high (on), feeding a 2-input AND gate with RCLK and inverted
CLKDS will do the same function. Figure 2 shows how to do this. MODE has two possibilities with the T5684 also:
* When MODE is at a logic level high (on) with the T5684, cutting the trace and bringing pin 5
to a logic level low will work with the LXT301Z. This is shown in Figure 1.
* When MODE is at a logic level low (off) with the T5684, Exar states in the data sheet that
RCLK is unrelated to RPOS and RNEG. If there is a need for this feature, call Applications Engineering at Intel for technical support.
Application Note
5
Replacing EXAR XR-T5684 with an LXT301Z Short-Haul Transceiver
Figure 1. Example of Similar Intel and Exar Circuits
EXAR T5684
8X or 16X CLK
VCC 5 9 10 26 1
VCC
LCLK MODE PD CLKDS TEST
1:1.36
TRING
1k
Level One Intel LXT301Z
1X CLK
1 5 9
1:2
MCLK TRING MODE XTALIN XTALOUT RLOOP LLOOP TTIP
n/c TTIP
10 26 27
n/c
27
Figure 2. CLKDS Logic
RCLKOUT
RCLK CLKDS
1.3
Analog Interface
The transformer turns ratio is different between the Exar T5684 and the LXT301Z LIU. The T1 transmit transformer turns ratio changes from 1:1.36 to 1:2 when using the LXT301Z. This is shown in Figure 1. Transformers with this turns ratio are readily available in drop-in replaceable packages. Please look at the Intel web site for more information about transformers at http:// www.developer.intel.com/design/network. The data sheets on our web site, have the latest information for the LXT301Z line interface unit.
1.4
Additional Advantages
Easier troubleshooting and simple upgrades come with the LXT301Z. Two diagnostic functions, local loopback and remote loopback, assist in finding circuit faults. Upgrading from the LXT301Z to the LXT304A is simple, since these LIU's are pin compatible. LXT304A features include reduced power consumption and jitter attenuation (with an external crystal) in either the transmit or the receive path. Please consult the distributor or Intel Technical Support for more solutions.
6
Application Note

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