Evaluation Board User Guide
UG-543
Rev. 0 | Page 5 of 16
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
EVAL-
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.
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
A
LK2
LK3
B
C
D
A
B
C
SHIELD
A
RO
RE
DE
DI
B
Z
Y
GND
RO
RE
DE
DI
L
K5
L
K6
A
B
Z
Y
GND
J1
J3
J2
VCC
EVAL-RS485FDEBZ
3.3V OR 5V
SUPPLY
SIGNAL
GENERATOR
1
1390-
004
Figure 4. Full-Duplex RS-485 Transceiver Loop Back Test
1
1390-
005
OSCILLOSCOPE
A
LK1
LK2
B
C
D
A
B
C
RO
RE
DE
DI
B
A
RO
RE
DE
DI
B
A
GND
J1
J3
VCC
A
LK1
LK2
B
C
D
A
B
C
SHIELD
RO
RE
DE
DI
B
A
GND
SHIELD
GND
RO
RE
DE
DI
L
K3
L
K4
L
K3
L
K4
B
A
GND
J1
J5
J5
J3
VCC
EVAL-RS485HDEBZ
EVAL-RS485HDEBZ
3.3V OR 5V
SUPPLY
3.3V OR 5V
SUPPLY
SIGNAL
GENERATOR
Figure 5. Half-Duplex RS-485 Two Board Point-to-Point Test
