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

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

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

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

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

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

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

RS485 = RS422 with tri-state drivers Used in multi-drop networks Data Communications (E&T2760): RS422, RS485, RS423, RS449 and V.35

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

RS422, RS423 Speed and Length Limits Source: Beyda, Basic Data Communications, Prentice Hall Data Communications (E&T2760): RS422, RS485, RS423, RS449 and V.35

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

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

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

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

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

Where to Get More Information www.sangoma.com/signal.htm www.arcelect.com/rs232.htm Data Communications (E&T2760): RS422, RS485, RS423, RS449 and V.35