Specifications

RS-422/485 Application Note 39
© 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]
EIA RS-232 Specification Summary
Parameter Conditions Min Max Units
Driver Output Voltage Open
Circuit
25 V
Driver Output Voltage Loaded
3 KΩ ≤ R
L
≤ 7 KΩ
5 15 V
V
Driver Output Resistance,
Power Off
-2V ≤ Vo ≤ 2V
300
Ω
Driver Output Short-Circuit
Current
500 mA
Driver Output Slew Rate 30
V/µs
Maximum Load Capacitance 2500 pF
Receiver Input Resistance
3V ≤ V
IN
≤ 25V
3000 7000
Ω
Receiver Input Threshold
Output = Mark
Output = Space
-3
3
V
V
EIA RS-423 Specification Summary
Parameter Conditions Min Max Units
Driver Output Voltage
Open Circuit
4
-4
6
-6
V
V
Driver Output Voltage
Loaded
R
L
= 450 Ω
3.6 6 V
Driver Output Resistance
-2V ≤ Vo ≤ 2V
50
Ω
Driver Output Short-
Circuit Current
±150 mA
Driver Output Rise and
Fall Time
Baud Rate ≤ 1K Baud
Baud Rate ≥ 1K Baud
300
30
µs
% Unit
Interval
Receiver Sensitivity
Vcm ≤ ±7V
±200 mV
Receiver Input Resistance 4000
Ω
40 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 B: EIA Standard RS-423 Data Transmission
RS-423 (EIA-423) is another standard used in point to point
communications. RS-423 data transmission uses an unbalanced line driver that
connects to an RS-422 type balanced line receiver as shown in Figure B.1.
The RS-423 line driver is unique to this system. It produces voltage similar to
RS-232 but has a slew rate control input that is used to limit rise times and
cross talk on the data lines. Typical adjustment on the slew rate control is
from 1 to 100 µs. This is done by the proper selection of one resistor on the
wave shape control input.
Figure B.1