P#9145-r1_485SD9TB-0812-1/2
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PRODUCT INFORMATION
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Model 485SD9TB
Port-Powered RS-485 Converter
The 485SD9TB is a port-powered two-channel RS-232 to RS-485 converter. It converts the TD and RD RS-232 lines to
balanced half-duplex RS-485 signals. The unit is powered from the RS-232 data and handshake lines whether the lines
are high or low. An external power supply can be connected to two terminals on the RS-485 connector if no handshake
lines are available. The 485SD9TB has a DB-9 female connector on the RS-232 side and a terminal block connector on
the RS-485 side.
RS-232 Side:
Connector:
DB-9
Female.
Signals:
Passes through pins 3 (TD) and 2 (RD).
Pins 7 (RTS) and 8 (CTS) are tied together.
Pins 4 (DTR), 6 (DSR), and 1 (CD) are tied together.
RS-485 Side:
Connector:
Terminal
Block
Signals:
Half-duplex two-wire operation only.
Automatic control circuit enables driver only when transmitting.
Receiver is disabled when transmitting to prevent echo back to RS-232 device.
Can transmit up to 4000 feet at 115.2k baud.
Power Requirements
No external power required if two RS-232 output handshake lines are available.
External 12VDC can be applied to pins on the RS-485 side between ter12VDC and GND if handshake lines are
not available.
35mA current draw maximum under normal operation when externally powered.
NOTE: When using an external supply, the supply should be connected only to specifically labeled
power inputs (power jack, terminal block, etc.). Connecting an external power supply to the
handshake lines may damage the unit. Contact technical support for more information on
connecting an external power supply to the handshake lines.
Dimensions:
3.50 x 1.34 x .67 in (8.9 x 3.4 x 1.7 cm)
Although the 485SD9TB uses handshake lines to power the converter, no handshaking is required to control the RS-
485 driver. The RS-485 driver is automatically enabled during each spacing state on the RS-232 side. During the
marking or idle state, the RS-485 driver is disabled and the data lines are held in the marking state by the 4.7K ohm
pull-up and pull-down resistors. The value of these resistors may need to be changed to a different value when
termination is used in order to maintain the proper DC bias during the idle state. See B&B Electronics’ RS-422/RS-485
Application Note for more information on termination and DC biasing of an RS-485 network.
The 485SD9TB has an internal connection to prevent data transmitted from the RS-232 port from being echoed back to
the RS-232 port. The 485SD9TB is used as a two wire (half duplex) RS-485 converter.
