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Model BB-485CON, RS-232 to RS-485 converter, converts unbalanced, full-duplex
RS-232 signals to balanced, full-duplex or half-duplex RS-485 signals. RS-485
is an enhanced version of the RS-422 balanced line standard. It allows multiple
drivers and receivers on a two-wire system.
The RS-232 port uses a male DB-25P type of connector with pins 2 (TD input) and
3 (RD output) supported. Protective Ground (pin 1) and Signal Ground (pin 7) are
also connected. The RS-485 port uses a female DB-25S type of connector with
Send Data outputs on pins 2 and 14, and Receive Data inputs on pins 5 and 17.
Protective Ground (pin 1) and Signal Ground (pin 7) are connected through to the
RS-232 connector.
CONNECTIONS
The polarity of the two RS-485 lines must be correct. With no data being sent, the
RS-232 line should be negative and the RS-485 “A” terminal should be negative
with respect to the “B” terminal. If your equipment uses a “+” and “-” naming
scheme, in most cases the “A” line will be connected to the “-” and the “B” line will
be connected to the “+”. The RS-485 driver must be enabled when checking the
polarity of the output of a RS-485 driver. On this connector, the RTS input (pin 4),
on the RS-232 side must be raised to enable the RS-485 driver.
Figure 1 shows how to interconnect two RS-485 converters using two signal wires.
The resistors Rt are optional, depending on the line length, baud rate, etc. The
resistors should be about the impedance of the line used, which is normally about
120 Ohms each. Termination resistors are installed only at each end of the RS-485
multidrop network. RTS must be off (low or marking) to receive and on (high or
spacing) to transmit. Both RTS’s should not be on at the same time. Although you
will not damage anything, the data sent will be garbled. If both RTS lines are off,
the line may be floating and random data may appear on the outputs. Your protocol
should allow for this if it can happen.
Up to 32 receivers can be driven by any one generator. This allows you to put
together large systems with many drop points. The termination resistors should be
located at approximately opposite ends of the system.
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General
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Mounting
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Power
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Serial Type
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Technology
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Features
- Convert unbalanced, full-duplex RS-232 to balanced, full-duplex or half-duplex RS-485
- Extend RS-232 data signals up to 1.2 km (4000 ft)
- 240 kbps baud rate (typical)
- Quick, easy inline installation
- Power supply required (not included, sold separately)
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