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Published byRussell Edwards Modified over 9 years ago
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RS422, RS485, RS423, RS449 and V.35 Data Communications (E&T2760): RS422, RS485, RS423, RS449 and V.35
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Introduction Serial interface standards that support longer cable lengths and higher data rate than RS232. Data Communications (E&T2760): RS422, RS485, RS423, RS449 and V.35
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Agenda Balanced Line Interface RS422 RS485 RS423 RS449 V.35
Data Communications (E&T2760): RS422, RS485, RS423, RS449 and V.35
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Vocabulary 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) Data Communications (E&T2760): RS422, RS485, RS423, RS449 and V.35
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Balanced (Differential) Line Interface
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 Data Communications (E&T2760): RS422, RS485, RS423, RS449 and V.35
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Balanced Line Interface
Data Communications (E&T2760): RS422, RS485, RS423, RS449 and V.35
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RS422 Balanced line interface
Mark: VA – VB > +0.2V Space: VA – VB < –0.2V Strictly for point-to-point communications Recommended maximum cable length is 4,000 ft. at 100kbps Data Communications (E&T2760): RS422, RS485, RS423, RS449 and V.35
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RS485 = RS422 with tri-state drivers Used in multi-drop networks
Data Communications (E&T2760): RS422, RS485, RS423, RS449 and V.35
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RS423 Single-ended (unbalanced) Mark: –3.6 to –6V Space: +3.6 to +6V
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 Data Communications (E&T2760): RS422, RS485, RS423, RS449 and V.35
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RS422, RS423 Speed and Length Limits
Source: Beyda, Basic Data Communications, Prentice Hall Data Communications (E&T2760): RS422, RS485, RS423, RS449 and V.35
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RS449 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 Data Communications (E&T2760): RS422, RS485, RS423, RS449 and V.35
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V.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 Data Communications (E&T2760): RS422, RS485, RS423, RS449 and V.35
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V.35 Connector Data Communications (E&T2760): RS422, RS485, RS423, RS449 and V.35
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V.35 Signals 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 S (Signal B) T U Terminal Timing V Receive Timing A W X Receive Timing Y Transmit Timing AA Data Communications (E&T2760): RS422, RS485, RS423, RS449 and V.35
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Summary 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 Data Communications (E&T2760): RS422, RS485, RS423, RS449 and V.35
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Where to Get More Information
Data Communications (E&T2760): RS422, RS485, RS423, RS449 and V.35
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