Robert Reay What V.35? V.35 CCITT recommendation data transmissio

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Robert Reay What V.35? V.35 CCITT recommendation data transmissio

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Interfacing V.35 Nertworks Design Note
Robert Reay
What V.35? V.35 CCITT recommendation data transmission 48kbs. electrical interface between data communication equipment (DCE) data terminal equipment (DTE) includes balanced differential circuits conforming Appendix Recommendation V.35 control circuits conforming Recommendation V.28 (equivalent RS232). typical V.35 interface uses five differential signals five single-ended handshaking signals. V.35 electrical specifications summarized Table
Table
Specification Source Impedance Common-Mode Impedance Voltage Swing Common-Mode Swing Common-Mode Range Condition Differential Measurement Terminals Shorted Load Load Between Grounds Transmitter Receiver 0.55V ±20% 0.6V
DN94
because output impedance driver well controlled. interface meet CCITT specifications under conditions, another approach needed. LTC®1345 LTC1345 single V.35 transceiver with three drivers three receivers that fully compliant with V.35 electrical specifications. chip configured operation shutdown using select pins. shutdown mode, supply current reduced 1µA. Each driver receiver terminated external resistor network (Figure guaranteeing compliance with V.35 impedance specification. transmitter output consists complementary switched-current sources 11mA shown Figure With test termination
Problems with Traditional Implementations tight tolerance transmitter's impedance voltage swing specifications makes implementation transmitter little tricky. traditional approach RS422 differential driver such AM26LS30 (Figure Because chip voltage output, signal must through resistive divider meet 0.55V swing specification. problem that output voltage function supply voltage, temperature processing, making tolerance swing hard meet conditions. Another problem meeting common-mode impedance specification
68.1 AM26LS30 68.1
DN94
Figure Termination Networks
11mA CHIP BOUNDARY
TEST TERMINATOR
DN94
11mA
Figure Simplified Transmitter Schematic
registered trademarks Linear Technology Corporation.
Figure Traditional V.35 Implementation
01/95/94
resistor, differential output voltage 0.55V (11mA 50), common-mode voltage thus meeting V.35 voltage swing specifications under conditions. five Y-termination resistor network single narrow body package available from Beckman Industrial (part number: Beckman 627T500/1250, phone: 714-447-2357). differential input receiver 40mV input hysteresis improve noise immunity common-mode range from 12V, allowing receivers used V.11 (RS422) applications, output forced into high impedance output enable (OE) when
VCC1 LTC1345 VCC1 627T500/ 1250 (SOIC)
receiver deselected. negative supply required meet common-mode operating range requirement. charge pump generates negative supply voltage (VEE) with three external capacitors allowing single operation. Complete V.35 Port Figure shows schematic complete single V.35 port using three eight capacitors port. LTC1345 with Beckman 627T500/1250 resistor network used transmit receive differential clock data signals. LT®1134 used transmit receive single-ended control signals.
VCC2 LTC1345
627T500/ 1250 (SOIC) (102) CABLE SHIELD
(103)
SCTE (113)
(114)
(115)
(104)
VCC2
LT1134
LT1134
(108)
(105)
(107)
(106)
(109)
OPTIONAL SIGNALS
(142)
(140)
(141)
2593 2593 34-PIN DTE/DCE 34-PIN DTE/DCE INTERFACE CONNECTOR INTERFACE CONNECTOR
DN94
Figure Complete Single V.35 Interface
literature Interface Products, call 1-800-4-LINEAR. applications help, call (408) 432-1900, Ext.
Linear Technology Corporation
1630 McCarthy Blvd., Milpitas, 95035-7487
(408) 432-1900 FAX: (408) 434-0507 TELEX: 499-3977
LT/GP 0195 160K PRINTED
LINEAR TECHNOLOGY CORPORATION 1995

Robert Reay What V.35? V.35 CCITT recommendation data transmissio

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