Specifications

RS-422/485 Application Note Table of Contents i
© Copyright B&B Electronics -- Revised 2506
B&B Electronics Mfg Co – 707 Dayton Rd - PO Box 1040 - Ottawa IL 61350 - Ph 815-433-5100 - Fax [phone]
B&B Electronics Ltd – Westlink Comm. Pk – Oranmore, Galway, Ireland – Ph 353-91-792444 – Fax [phone]
Table of Contents
CHAPTER 1: OVERVIEW............................................................................... 1
I
NTRODUCTION ................................................................................................. 1
D
ATA TRANSMISSION SIGNALS......................................................................... 1
Unbalanced Line Drivers............................................................................. 1
Balanced Line Drivers................................................................................. 1
Balanced Line Receivers.............................................................................. 3
EIA
STANDARD RS-422 DATA TRANSMISSION ................................................ 3
EIA
STANDARD RS-485 DATA TRANSMISSION ................................................ 6
T
RISTATE CONTROL OF AN RS-485 DEVICE USING RTS................................... 9
S
END DATA CONTROL OF AN RS-485 DEVICE................................................ 11
CHAPTER 2: SYSTEM CONFIGURATION .............................................. 13
N
ETWORK TOPOLOGIES .................................................................................. 13
T
WO WIRE OR FOUR WIRE SYSTEMS.............................................................. 13
T
ERMINATION................................................................................................. 16
B
IASING AN RS-485 NETWORK ...................................................................... 17
E
XTENDING THE SPECIFICATION..................................................................... 19
CHAPTER 3: SELECTING RS-422 AND RS-485 CABLING ................... 20
N
UMBER OF CONDUCTORS ............................................................................. 20
S
HIELDING...................................................................................................... 20
C
ABLE CHARACTERISTICS .............................................................................. 20
CHAPTER 4: TRANSIENT PROTECTION OF RS-422 AND RS-485
SYSTEMS......................................................................................................... 23
W
HAT DOES A SURGE LOOK LIKE? .................................................................. 23
Surge Specifications................................................................................... 23
Common Mode vs. Differential Mode........................................................ 25
G
ROUND ≠ GROUND .......................................................................................26
T
RANSIENT PROTECTION USING ISOLATION .................................................... 27
Isolation Theory......................................................................................... 27
Isolation Devices........................................................................................ 28
T
RANSIENT PROTECTION USING SHUNTING .................................................... 28
Shunting Theory......................................................................................... 28
Connecting Signal Grounds.......................................................................29
Shunting Devices........................................................................................ 29
C
OMBINING ISOLATION AND SHUNTING ......................................................... 29
S
PECIAL CONSIDERATION FOR FAULT CONDITIONS........................................ 31
C
HOOSING THE RIGHT PROTECTION FOR YOUR SYSTEM................................... 31
ii Table of Contents RS-422/485 Application Note
© Copyright B&B Electronics -- Revised 2506
B&B Electronics Mfg Co – 707 Dayton Rd - PO Box 1040 - Ottawa IL 61350 - Ph 815-433-5100 - Fax [phone]
B&B Electronics Ltd – Westlink Comm. Pk – Oranmore, Galway, Ireland – Ph 353-91-792444 – Fax [phone]
CHAPTER 5: SOFTWARE........................................................................... 33
I
NTRODUCTION ............................................................................................... 33
RS-422
SYSTEMS............................................................................................ 33
RS-485
DRIVER CONTROL.............................................................................. 33
RS-485
RECEIVER CONTROL..........................................................................34
M
ASTER-SLAVE SYSTEMS .............................................................................. 34
Four Wire Master-Slave Systems............................................................... 34
Two Wire Master-Slave Systems................................................................ 34
M
ULTI-MASTER RS-485 SYSTEMS ................................................................. 35
S
YSTEMS WITH PORT POWERED CONVERTERS................................................ 35
CHAPTER 6: SELECTING RS-485 DEVICES.......................................... 36
CHAPTER 7: SOURCES OF FURTHER INFORMATION.....................37
APPENDIX A: EIA SPECIFICATION SUMMARY ................................. 38
APPENDIX B: EIA STANDARD RS-423 DATA TRANSMISSION........40