Serial Communication Converters & Adapters Instruction Manual
13
PDA7485 RS-232 to RS-
422/485 Converter
Description
The PDA7485 converts unbalanced, full-duplex
RS-232 signals to balanced, full or half-duplex
RS-422 or RS-485 signals.
The RS-232 port, configured as a DTE port, has
a female DB9 connector with pins 2 (RX output),
3 (TX input), and 5 (Signal Ground). Pins 7
(RTS) and 8 (CTS) are tied together, and pins 1
(CD), 4 (DTR), and 6 (DSR) are tied together.
The RS-485 terminal blocks support Transmit
Data (DO) and (/DO), Receive Data (DI) and
(/DI), and Signal Ground. A separate terminal
block supports the power input (+12VDC) and
power ground (GND).
Baud rates are automatic and handled by the
PDA7485.
The PDA7485 has three diagnostic LEDs: a
Power (P) LED to show when the converter is
powered properly, a Transmit Data (TX) LED to
show when the converter is sending data out
from the PC side, and a Receive Data (RX) LED
to show when the converter is receiving data
from the network side.
The DIP switch SW1 is located between the
screw terminal connectors and allows for system
configurations.
Installation
The DIP switch SW1 allows for several different
options. Factory settings for the switch are shown in
Figure 13.
1 2 3 4 5
Figure 13. PDA7485 Terminal Connectors
and DIP Switch
The TERM switch position adds an internal 120
ohm termination resistor when ON (up).
Termination should be used on both ends of the
network with high data rates and long wiring
runs.
To configure a two-wire network set both of the
2 WIRE switch positions to ON (up). For a four-
wire network set both of the 2 WIRE switches to
OFF (down).
When the RS422 switch position is ON (up) it is
configured for an RS-422 network. For RS-485
networks set the RS422 switch to OFF (down).
The ECHO switch position allows the data being
sent from the RS-232 port to be echoed back
into the RS-232 port. In most networks, this is an
undesired effect and the ECHO switch would be
OFF (down).
PDA7485 DIP Switch Settings
SW1 Switch
Position
ON Setting Function
1
Network Termination
Included (120 ohm)
2
2-Wire Network Mode
Connection (factory
setting)
3
2-Wire Network Mode
Connection (factory
setting)
4
RS-422 Mode
5
ECHO Mode
Figure 14. PDA7485 DIP Switch Settings
Figure 15 shows an example configuration of a
two-wire network. Each device (e.g. Trident
PD765 meter) connected to the same network
must have a unique address.
