Half-Duplex RS-485-/RS-422-Compatible
Transceiver with AutoDirection Control
V
CC
V
CC
DI
D
DI
D
R
R
t
t
SHDN
SHDN
V
V
CC
CC
RO
RE
RO
RE
R
R
MAX13487E
MAX13488E
R
R
D
D
DI SHDN RO RE
DI
RO RE
SHDN
Figure 11. Typical Half-Duplex RS-485 Network
Circuit shows an isolated RS-485 interface using the
MAX13487E/MAX13488E. The transceiver is powered
separately from the controlling circuitry. The
AutoDirection feature of the MAX13487E/MAX13488E
(see the AutoDirection Circuitry section), replaces an
external relay allowing faster switching speeds, no con-
tact bounce, better reliability, and better electrical isola-
tion. The MAX13487E/MAX13488E only require two
optocouplers to electrically isolate the transceiver.
Typical Applications
The MAX13487E/MAX13488E transceivers are
designed for half-duplex, bidirectional data communi-
cations on multipoint bus transmission lines. Figure 11
shows a typical networꢀ application. To minimize reflec-
tions, terminate the line at both ends in its characteristic
impedance, and ꢀeep stub lengths off the main line as
short as possible. The slew-rate-limited MAX13487E is
more tolerant of imperfect termination.
Isolated RS-485 Interface
An isolated RS-485 interface electrically isolates differ-
ent nodes on the bus to protect the bus from problems
due to high common-mode voltages that exceed the
RS-485 common-mode voltage range, conductive
noise, and ground loops. The Typical Application
Chip Information
PROCESS: ꢂiCMOS
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