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OVERVIEW
Model BB-485PTBR converts unbalanced RS-232 signals to balanced, full or
half-duplex RS-485 signals. RS-485 is an enhanced version of the RS-422
Standard allowing multiple drivers and receivers on a two-wire system. The
RS-232 port has a female DB9 connector with pins 2(RD), 3(TD), and 5(SG)
supported. Pins 7(RTS) and 8(CTS) are tied together. Also pins 6(DSR),
1(CD), and 4(DTR) are tied together, but not passed through the converter.
The RS-485 port has an 8-position pluggable terminal block connector.
BAUD RATE
Model BB-485PTBR supports baud rates from 300 to 115.2K. In order to
change the baud rate, a resistor and possibly a capacitor must be changed.
By looking up the selected baud rate on Table 1 the resistor and capacitor
value can be determined. Remove R3 and C7 from the printed circuit board.
Place new components in the R2 and C6 locations. See Figure 1 and 2 for
resistor and capacitor locations.
BIASING RESISTORS
The biasing resistors R5 and R7 can also be altered. Model BB-485PTBR
comes standard with 4.7K biasing resistors. To change the value of biasing
resistors, remove R5 and R7 and replace with new value in locations R4 and
R6. See Figures 1 and 2 for resistor locations.
TERMINATION RESISTOR
The termination resistor is located at R8. A termination resistor can be
placed in the R8 location and a jumper wire placed from the terminal
location to RD(B). B+B SmartWorx recommends a 100-120 Ohm resistor for
termination. See Figure 2 for termination resistor location.
CONSTANT RECEIVER ENABLE
The BB-485PTBR is factory-set with the receiver disabled during
transmission. It can be set for constant receiver enable. When R9 is
removed, the receiver is in constant receive mode (four-wire). When R9 is
in the circuit it is in half-duplex mode (two-wire). See Figure 1 for jumper
location.
DATA LINE POLARITY
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 “+”.
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Category
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Attribute
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Value
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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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