20µA,
1
⁄
8
-Unit-Load, Slew-Rate-Limited
RS-485 Transceivers
MAX1482/MAX1483
Line Length vs. Data Rate
5
DI
0
The RS-485/RS-422 standard covers line lengths up to
4000 feet. For line lengths greater than 4000 feet, see
Figure 16.
Figure 13 shows the system differential voltage for the
parts driving 4000 feet of 26AWG twisted-pair wire at
110kHz into 120Ω loads. Even after 4000 feet of cable,
the MAX1482/MAX1483 output shows virtually no dis-
tortion.
1
RECEIVER
INPUT
V
Y
-V
Z
0
Typical Applications
-1
5
R
O
0
2µs/div
Figure 13. System Differential Voltage at 250kbps (125kHz)
Driving 4000 Feet of Cable
The MAX1482/MAX1483 transceivers are designed for
bidirectional data communications on multipoint bus
transmission lines. Figures 14 and 15 show typical net-
work applications circuits. These parts can also be
used as line repeaters, with cable lengths longer than
4000 feet, as shown in Figure 16.
To minimize reflections, the line should be terminated at
both ends in its characteristic impedance, and stub
lengths off the main line should be kept as short as
possible (although the slew-rate-limited MAX1482 and
MAX1483 are more tolerant of imperfect termination
than standard RS-485 ICs).
Isolated RS-485
For isolated RS-485 applications, see the MAX253 and
MAX1480 data sheets.
120Ω
DI
B
120Ω
B
DE
D
DE
RO
RE
A
B
A
B
A
A
D
DI
R
R
D
D
R
R
RO
RE
MAX1483
DI
DE
RO RE
DI
DE
RO RE
Figure 14. MAX1483 Typical Half-Duplex RS-485 Network
10
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