~ National ~ Semiconductor - Al Kossow's Bitsavers

Differential Data Transmission (Continued)
r--....
>
EIA RS·422 Application
r-INTERFACE
RS422 -=:1
~> >~
DATA 0- DATA
IN
.m~.~~
» »
- - TL/OO/2901-3
OUT
The key features of RS-485:
• Drivers can withstand bus contention and bus faults
• Implements a truly multipoint bus consisting of up to 32 National Semiconductor produces a variety of drivers, redrivers
and 32 receivers
ceivers, and transceivers for these four very popular trans-
• An extended common-mode range for both drivers and mission standards and numerous other data transmission
receivers in TRI-STATE and with power off (-7V to requirements.
+ 12V) Shown below is a table that highlights key aspects of the
EIA Standards. More detailed comparisons can be found in
the various application notes in Section 1.
O-Driver
RS·485 Application
A)';~ ~ A \\{
\Ij
" //
i "
"" ~ RT
"" I
120 RT ~
120
OHMS
OHMS
R - Receiver
T - Transceiver V
" "
"" IL\
T I()\
\;j
TL/OO/2901-4
Specification RS·232C RS·423 RS·422 RS·485
Mode of Operation Single-Ended Single-Ended Differential Differential
Number of Drivers and Receivers 1 Driver, 1 Driver, 1 Driver, 32 Drivers,
Allowed on One Line 1 Receiver 10 Receivers 10 Receivers 32 Receivers
Maximum Cable Length 50 feet 4000 feet 4000 feet 4000 feet
Maximum Data Rate 20 kb/s 100 kb/s 10 Mb/s 10 Mb/s
Driver Output Maximum Voltage ±25V ±6V -0.25Vto +6V -7Vto +12V
Driver Output Signal Level I Loaded ±5V ±3.6V ±2V ±1.5V
J
Unloaded ±15V ±6V ±5V ±5V
Driver Load Impedance 3 k.fl to 7 k.fl 450.fl min 100.fl 54.fl
Maximum Driver Output Current I Power On ---- ---- ---- ±100,...A
(High Impedance State)
I Power Off VMAX/ 3OO.fl ±100 ,...A ± 100,...A ±100 ,...A
Slew Rate 30V/,...smax Controls Provided ---- ----
Receiver Input Voltage Range ±15V ±12V -7Vto +7V -7Vto +12V
Receiver Input Sensitivity ±3V ±200mV ±200mV ±200mV
Receiver Input Resistance 3 k.fl to 7 k.fl 4 k.fl min 4 k.fl min 12 k.fl min
6-4