Specifications

RS-422/485 Application Note 37
© 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 7: Sources of Further Information
EIA Standards and Publications can be purchased from:
GLOBAL ENGINEERING DOCUMENTS
7730 Carondelet Avenue
Clayton, MO 63105
Phone: [phone]
FAX: [phone]
GLOBAL ENGINEERING DOCUMENTS
15 Inverness Way East
Englewood, CO 80112
Phone: [phone]
FAX: [phone]
Global Engineering Documents web site can be found at http://global.ihs.com.
Related data interface standards are:
a) EIA-232-E Interface between data terminal equipment and date circuit-
terminating equipment employing serial binary data
interchange (ANSI/IEA-232-D)
b) EIA-422-A Electrical characteristics of balanced voltage digital interface
circuits
c) EIA-423-A Electrical characteristics of unbalanced voltage digital interface
circuits
d) EIA-485 Standard for electrical characteristics of generators and
receivers for use in balanced digital multipoint systems
e) EIA-449 General purpose 37-position and 9-position interface for data
terminal equipment and data circuit-terminating equipment.
f) EIA-530 High speed 25-position interface for data terminal equipment
and data circuit-terminating equipment
g) EIA/TIA-562 Electrical characteristics for an unbalanced digital interface
Manufacturers of integrated circuit data transceivers often offer practical
application information for RS-422 and RS-485 systems.
National Semiconductor’s Interface Data Book includes a number of excellent
applications notes. These notes are also available online at
http://www.national.com/
. A search engine is provided to search the text of the
available application notes. Entering “422” or “485” as search criteria to get a
current list of related application notes.
38 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]
Appendix A: EIA Specification Summary
EIA RS-422 Specification Summary
Parameter Conditions Min Max Units
Driver Output Voltage
Open Circuit
10
-10
V
V
Driver Output Voltage
Loaded
R
T
= 100 Ω
2
-2
V
V
Driver Output Resistance A to B 100
Ω
Driver Output
Short-Circuit Current
Per output to
common
±150 mA
Driver Output Rise Time
R
T
= 100 Ω
10 % of Bit Width
Driver Common Mode
Voltage
R
T
= 100 Ω
±3 V
Receiver Sensitivity
Vcm ≤ ±7
±200 mV
Receiver Common-Mode
Voltage Range
-7 +7 V
Receiver Input Resistance 4000
Ω
Differential Receiver
Voltage
Operational:
Withstand:
±10
±12
V
V
EIA RS-485 Specification Summary
Parameter Conditions Min Max Units
Driver Output Voltage
Open Circuit
1.5
-1.5
6
-6
V
V
Driver Output Voltage
Loaded
R
LOAD
= 54Ω
1.5
-1.5
5
-5
V
V
Driver Output Short-
Circuit Current
Per output to
+12V or –7V
±250 mA
Driver Output Rise Time
R
LOAD
= 54Ω
C
LOAD
= 50 pF
30 % of Bit Width
Driver Common Mode
Voltage
R
LOAD
= 54Ω
-1 3 V
Receiver Sensitivity
-7 ≤ Vcm ≤ +12
±200 mV
Receiver Common-Mode
Voltage Range
-7 +12 V
Receiver Input Resistance 12K
Ω