RS422,%20RS485,%20RS423,%20RS449%20and%20V.35

1
RS422, RS485, RS423, RS449 and V.35
2
Introduction

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

3
Agenda

• Balanced Line Interface
• RS422
• RS485
• RS423
• RS449
• V.35

4
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)

5
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

6
Balanced Line Interface
7
RS422

• Balanced line interface
• Mark VA VB gt 0.2V
• Space VA VB lt 0.2V
• Strictly for point-to-point communications
• Recommended maximum cable length is 4,000 ft. at
  100kbps

8
RS485

• RS422 with tri-state drivers
• Used in multi-drop networks

9
RS423

• 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

10
RS422, RS423 Speed and Length Limits
Source Beyda, Basic Data Communications,
Prentice Hall
11
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

12
V.35

• V.10 V.11
• Widely used to connect high speed (gt 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

13
V.35 Connector
14
V.35 Signals
15
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

16
Where to Get More Information

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