data communications (e&t2760): rs422, rs485, rs423, rs449 and v.35 1 rs422, rs485, rs423, rs449...

Data Communications (E&T2760): RS422, RS485, RS423, RS449 and V.35

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RS422, RS485, RS423, RS422, RS485, RS423, RS449 and V.35RS449 and V.35


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Introduction Introduction

Serial interface standards that support longer cable lengths and higher data rate than RS232.


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AgendaAgenda

Balanced Line InterfaceRS422RS485RS423RS449V.35


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VocabularyVocabulary

Skew Rate– Measure the slope of signal transitions

between Mark and Space– High skew rate causes interference to adjacent

wires within the same cable (i.e. crosstalk)


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Balanced (Differential) Line Balanced (Differential) Line InterfaceInterface A pair of wires is used to carry each signal. The

data is encoded and decoded as a differential voltage between the two lines

Advantages:– the interface is unaffected by differences in ground

voltage between sender and receiver

– if lines A and B are close together (e.g. in twisted pairs), they will be affected almost identically by external electromagnetic noise, which can then be eliminated at receiver


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Balanced Line InterfaceBalanced Line Interface


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RS422RS422

Balanced line interface– Mark: VA – VB > +0.2V

– Space: VA – VB < –0.2V

Strictly for point-to-point communicationsRecommended maximum cable length is

4,000 ft. at 100kbps


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RS485RS485

= RS422 with tri-state driversUsed in multi-drop networks


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RS423RS423 Single-ended (unbalanced)

– one pair of wires per signal, one of it is GND– crosstalk is further reduced by using lower signal

skew rate Mark: –3.6 to –6V Space: +3.6 to +6V Can be used in one-to-many-points

communications Recommended maximum cable length is 40ft. at

100kbps, for 10 receivers


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RS422, RS423 Speed and Length RS422, RS423 Speed and Length LimitsLimits

Source: Beyda, Basic Data Communications, Prentice Hall


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RS449RS449

Replace RS232 in high speed synchronous communication between DTE and DCE

Combine both balanced and unbalanced signals on the same interface– RS422: for fast changing signals like TD, RD

and Clock– RS423: for slow changing signals like RTS,

CTS, DSR, DTR, … etc.Use a DB37 connector


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V.35V.35

= V.10 + V.11 Widely used to connect high speed (> 56kbps)

DCEs in WAN (e.g. T1, Frame Relay, ATM networks)

Combine both balanced and unbalanced signals on the same interface– RS422: for fast changing signals like TD, RD and

Clock– RS232: for slow changing signals like RTS, CTS,

DSR, DTR, … etc. Easily recognized by it bulky 34-pin connector


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V.35 ConnectorV.35 Connector


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V.35 SignalsV.35 SignalsPin Signal Pin Signal

A Chassis Ground B Signal Ground

C Request to Send D Clear to Send

E Data Set Ready F Receive Line Signal Detect

H Data Terminal Ready J Ring Indicator

P Transmitted Data(Signal A)

R Received Data(Signal A)

S Transmitted Data(Signal B)

T Received Data(Signal B)

U Terminal Timing V Receive Timing A

W Terminal Timing X Receive Timing

Y Transmit Timing AA Transmit Timing


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SummarySummary

RS422 and RS423 support longer cable length at higher data rates than RS232– RS422: benefit from balanced line interface

– RS423: benefit from individual ground return and lower skew rate

RS449 and V.35 combine both balanced and unbalanced signals on the same interface– RS449: RS422 + RS423

– V.35: RS422 + RS232


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Where to Get More InformationWhere to Get More Information

www.sangoma.com/signal.htmwww.arcelect.com/rs232.htm

data communications (e&t2760): rs422, rs485, rs423, rs449 and v.35 1 rs422, rs485, rs423, rs449...

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