Analog Devices EVAL-RS485HDEBZ User Manual page 5

Evaluation Board User Guide
Connecting to an Existing RS-485 Network
For a two-wire connection to an existing RS-485 network,
driver enable (DE) should be disabled (LK2 for
RS485HDEBZ, LK3 for EVAL-RS485FDEBZ) by moving to
Position B, or else should be controlled externally (Position C)
based on received data.
For a four-wire connection using EVAL-RS485FDEBZ, the
driver can be permanently enabled by placing LK3 in Position A,
if the Y and Z connections are connected only to RS-485
receivers. Otherwise, LK3 should be in Position B or Position C.
3.3V OR 5V
SUPPLY
J1
GND
J3
LK1
RO
A
RO
B RE
C
RE
DE
D
DE
A
DI
B
DI
C
LK2
EVAL-
SIGNAL
3.3V OR 5V
GENERATOR
SUPPLY
J1
GND VCC
J2
LK2
RO A
A
RO
B RE B
C
RE
DE
D
Z
DE
A
DI Y
DI
B
C
LK3
Figure 4. Full-Duplex RS-485 Transceiver Loop Back Test
SIGNAL 3.3V OR 5V
GENERATOR SUPPLY
J1
GND
J3
LK1
RO
A
RO
B RE
C
RE
DE
D
DE
A
DI
DI
B
C
LK2
EVAL-RS485HDEBZ
VCC
J5
B
B
A
A
SHIELD
GND
Figure 5. Half-Duplex RS-485 Two Board Point-to-Point Test
Rev. 0 | Page 5 of 16
For a four-wire connection using EVAL-RS485FD8EBZ, the Y
and Z connections should only be connected to other RS-485
receiver inputs, as shown in Figure 6 for a multinode bus.
These full-duplex parts without driver or receiver enable inputs
can also typically be used in point-to-point four-wire RS-485
bus connections.
OSCILLOSCOPE
EVAL-RS485FDEBZ
J3
A
B
Z
Y
SHIELD
GND
EVAL-RS485HDEBZ
VCC
J5
B
B
A
A
SHIELD
GND
UG-543
OSCILLOSCOPE