Crystal-less Long-Haul Solutions LXT318/360 Universal Line Interf

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Crystal-less Long-Haul Solutions LXT318/360 Universal Line Interf

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LXT318/360 Universal Line Interface Unit Design Guide
Introduction
This note describes applications crystal -less LXT360 transceiver newer generation network access equi pment. this application note when upgrading designs using LXT360. Before designi circuit using this device, refer data sheets both devices complete information. LXT360 provides several advanced features. While LXT360 provides both (1.544 Mbps) (2.044 Mbps) operati this application note focuses only hardware-controlled, designs. Additi onal application notes detail migration paths design using other LXT360 features.
Identifying Major LXT360 Design Improvements
Jitter Attenuation Circuitry LXT318 devi requires pullabl 8.192 crystal provi selectable jitter attenuation. jitter attenuati circuitry ther transmit recei path, depending application. LXT360 requires only MCLK signal provide same selectabl jitter attenuation functions since uses digital circui try. needs crystal high-frequency external clock jitter attenuati Output Control LXT318 provi high-impedance state option TTIP/ outpu only grounded. LXT360 provides high-impedance state limited TTIP/TRING tputs TCLK pulled High. addi onal high-impedance state option available output when TRSTE pulled High. LXT318 provides Line Attenuati Indi cation (LATN) both Hardware Host Modes. LXT360 provides LATN Software Mode only. LXT318 transceiver, holding LLOOP TAOS High simultaneousl then pulling three enabl LOOP detection unction Alternatively, tying RCLK RLOOP also enables NLOOP. Resetting device disables NLOOP detection. LXT360 setting RLOOP nput ±0.2 ("Midrange") enables NLOOP detection. Setting RLOOP disables NLOOP detection. LXT318 device declares Loss Signal (LOS) conditi when detects consecutive spaces. ears condition when receiver detects 12.5% mark density (i.e., marks within 32-bit period) more than consecutive LXT360 transceiver declares condition when detects consecutive spaces. clears conditi when recei detects 12.5% mark density (i.e., marks within 32-bit period) more than consecutive
External Clock Requirements MCLK input signal LXT318 optional used, clock must have accuracy ±100 ppm. MCLK input signal LXT360 mandatory. clock must stand alone reference accuracy better 2.048 applicati ons.
Line Attenuation Indication
NLOOP Detection
Applications LXT318 long-haul transcei only. LXT360 operates either short- long-haul transceiver applications.
Available Line Coding Schemes LXT318 allows HDB3 encoding either Unipolar polar mode. LXT360 transcei offers HDB3 encoding polar Mode.
Loss Signal Detection Clear Criteria
Reset Operation Reset LXT318 occurs when both LLOOP RLOOP inputs High while TAOS pulled least Reset LXT360 occurs when LLOOP, RLOOP TAOS High simultaneously east
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DIAGNOSTIC FUNCTIONS
LXT360 provides several diagnostic features provided LXT318 transceiver. These Dual Loopback function, Error Insertion Detection, Condition Monitoring Elastic Store Pointer Monitoring. Refer LXT360 data sheet details these functions. addition, LXT360 provides both Quasi-Random Signal Source Detector diagnostic procedures.
Tables through show combinations transformers, resistors capacitors needed transmit side shown these applications. Table lists transformers that meet Level Communications specifications when tested with LXT360 device.
Table Transmit Return Loss (2.048 Mbit/s-Short-Haul
Xfrmr/ 1:2/ Xmission Line Coax Twisted Pair 1:2.3/ Twisted Pair (pF) Return Loss (dB)
EC4-1 1000
Three-State Input Pins
LXT318 uses two-state (High Low) configuration inputs some LXT360 control inputs recognize three states. Typical values these states are: High-VIN Midrange-2.3 floating). Low-VIN control three-state inputs standard tristate buffer. Figure shows typical driver circuit these inputs. Setting output buffer high-impedance state places three-state input into Midrange state. Application designers must take into account current drawn internal resistors (part each three-state input) before choosing buffer drive these inputs their High states.
Table Transmit Return Loss (2.048 Mbit/s-Long-Haul High
Return Loss Configuration Xfrmr/ 1:2/ 1:1.53/ Xmission Line Twisted Pair Coax (pF) Return Loss (dB)
EC4-1 1001
Figure Typical Circuit LXT360 Three-State Inputs
LXT360
Table Transmit Return Loss (2.048 Mbit/s-Long-Haul
Xfrmr 1:2/ Xmission Line Twisted Pair Coax (pF) Return Loss (dB)
buffer with tri-state output Typical 3-State Input
EC4-1 1010
Line Interface Considerations
improve transmit return loss, capacitor transmit side shown Figures through This capacitor typically vary depending resistor transformer values, board layout parasitics protection diodes.
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Crystal-less Long-Haul Solutions Table Recommended Transformers LXT360
Transmit Side Transformer Turns Ratio Manufacturer Fil-Mag HALO Midcom Pulse Engi neeri Schott Corp 1:1.53 Pulse Engi neeri Part Number 66Z1308 61-1205G 67-1205G 671-5832 PE-65351 PE-65771 67127370 67130850 68663 Transformer Turns Ratio Receive Side Manufacturer Fil-Mag HALO Midcom Pulse Engineering Schott Corp Part Number 80006-155 61-1205G 67-1205G 671-5792 PE-64936 PE-65778 67109150 67130840
Bipolar Mode with Line Coding (without Zero Suppression)
Most pins LXT360 have same names functions those LXT318, though some differ. This section descri modifications needed change from LXT318 LXT360 Hardware Control Mode. LXT360 pins included this discussion have same connections signal level requirements those LXT318. Table summary pins whose functions change when moving from LXT318 LXT360. 8.192 crystal required LXT318 must deleted when migrating LXT360. functions pins LXT318 change locations LXT360 transceiver. particular attention locations these signals. Figure shows connection differences between transcei vers this configuration. LXT360 requires independent, external clock called MCLK. MCLK input signal must have nominal rate 2.048 accuracy better. LXT318 uses same nomi frequency, requires better accuracy than ±100 ppm. LXT318, called MODE. pulled Low, tied RCLK pin. RCLK signal MODE enables HDB3 encoders decoders. LXT360, MODE three-state input pin: High, Midrange. Setti Midrange enables HDB3 encoders decoders LXT360 applications (and forces transceiver into unipolar operation).
LXT360, called TRSTE. threestate input. With TRSTE pulled High LXT360 devi output pins into gh-impedance state. conj uncti MODE (pin also sets operational mode transceiver. enable Long-Haul dB), Bipolar, Hardware Control Mode, TRSTE must pulled Low. data sheet complete description operati modes. This XTALOUT input LXT318. Leave this connected LXT360. grounded LXT318 applications. LXT360, (EC4) enable longhaul operation. LXT318 signal (NLOOP) appears LXT360. LATN signal, which LXT318, available Hardware Mode LXT360. However, binary encoded equi valent LATN provi LXT360 Software Mode. NLOOP signal, which appears LXT318, avai lable LXT360. Pins LXT318, pins both grounded. LXT360 uses these pins gives them names (pin (pin 25). EC4-1 control equalizers LXT360. LXT360 Data Sheet detai
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Crystal-less Long-Haul Solutions Figure Bipolar Mode Using Line Coding (without Zero Suppression)
LXT318
MCLK MODE 8.192 XTALOUT TTIP NLOOP TRING NLOOP XTALIN
LXT360 2.048 Clock
MCLK
MODE
TRSTE
TTIP
TRING LATN NLOOP
NOTE: Pins shown figure have same function both LXT318 LXT360. They require modificati proper functioning.
Table Bipolar Mode using Line Coding (without Zero Suppression)
LXT318 Pin# Name MCLK1 MODE XTALIN LATN NLOOP Function/State 2.048 MHz/GND Name MCLK MODE LXT360 Function/ State 2.048 Input-High Output Input Input Input/Low Comments Mandatory LXT360 applications MODE TRSTE operation mode Crystal used LXT360 function assigned this pin. operation. LATN supported LXT360 Hardware Control Mode. NLOOP changes location. Refer Table LXT360 Data Sheet.
8.192 Crystal TRSTE NLOOP Output Output
XTALOUT 8.192 Crystal
1.MCLK optional LXT318 applications. With LXT318, MCLK supplied, must grounded.
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Using HDB3 Encoding/Decoding
LXT318 supports HDB3 encoding/decoding both Unipolar Bipolar Modes. LXT360 configures tself polar mode (i.e., TPOS becomes TDATA TNEG becomes INSBPV) when HDB3 enabled. enable HDB3 encoders decoders, MODE Midrange. Other connections same line coding. Figure shows changes needed connections LXT318 LXT360. Table summary modifi cations needed adapt LXT318 application LXT360.
Figure Unipolar Mode (with HDB3 Zero Suppression)1
LXT318
MCLK MODE
LXT360 2.048 Clock
MCLK
MODE RCLK TRSTE TTIP
Midrange
RCLK
8.192
XTALIN TTIP NLOOP
XTALOUT
TRING NLOOP
TRING LATN NLOOP
NOTE: Pins shown this figure have same function both LXT318 LXT360. They require modificati proper functioning.
Table Unipolar Mode with HDB3 Zero Suppression Enabled
LXT318 Pin# Name MCLK
LXT360 Name MCLK MODE TRSTE Function/State 2.048 Midrange2 Input-High High operation LATN supported LXT360 Hardware Control Mode. NLOOP changes location. Refer Table LXT360 Data Sheet. Comments Mandatory LXT360 applications MODE TRSTE operation mode Crystal used LXT360
Function/State 2.048 MHz/GND RCLK 8.192 Crystal Output Output
MODE XTALIN LATN NLOOP
XTALOUT 8.192 Crystal
NLOOP Output Input Input Input/Low
1.MCLK opti onal LXT318 applications. With LXT318, MCLK supplied, must grounded. 2."Midrange" means leave unconnected
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ENABLING NLOOP DETECTION Tying RLOOP MODE inputs RCLK output enables Network Loop detection (NLOOP) LXT318 transceiver. NLOOP also enabled holding LLOOP, RLOOP, TAOS High simul taneously pulling them Low. enable NLOOP LXT360 transceiver, RLOOP input Midrange Figure This functi available only Bipolar Mode.
Figure Bipolar Mode
LXT318
MCLK RCLK MODE RLOOP RCLK
LXT360 2.048 Clock
MCLK MODE TRSTE RLOOP TTIP NLOOP TRING NLOOP Midrange RCLK
8.192
XTALIN TTIP
XTALOUT
TRING LATN NLOOP
NOTE: shown figure have same function both LXT318 LXT360. They require modification proper functi oning.
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Crystal-less Long-Haul Solutions LXT318/360 Universal Line Interf

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