Document No. 485PTBR4500 - pg. 1/2
1996 B&B Electronics -- Revised November 2000
This product designed and manufactured in USA of domestic and imported parts by
RS-232 to RS-485 Converter
CE
Model 485PTBR
Description
The 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. It allows multiple
drivers and receivers on a two-wire system. The RS-232 port has a female DB-9 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
The 485PTBR can accept baud rates from 300 baud to 115.2K baud. In order to change the baud rate on the
485PTBR 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. The 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
Figure 1 and 2 for resistor locations.
Termination Resistor
The termination resistor location for the 485PTBR 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). We recommend a value of 100 to 120 ohm resistor
for termination. See Figure 2 for termination resistor location.
Constant Receiver Enable
The 485PTBR is standard setup with the receiver disabled during transmission. The 485PTBR can be set up for
constant receiver enable. When R9 is removed the receiver is in constant receive mode (four-wire). When R9 is in the
circuit the 485PTBR 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 "+".
DECLARATION OF CONFORMITY
Manufacturer's Name:
B&B Electronics Manufacturing Company
Manufacturer's Address:
P.O. Box 1040
707 Dayton Road
Ottawa, IL 61350 USA
Model Number:
485PTBR
Description:
RS-232 to RS-485 Converter
Type:
Light industrial ITE equipment
Application of Council Directive: 89/336/EEC
Standards:
EN 50082-1 (IEC 801-2, IEC 801-3, IEC 801-4)
EN 50081-1 (EN 55022, IEC 1000-4-2)
EN 61000 (-4-2, -4-3, -4-4, -4-5, -4-6, -4-8, -4-11)
ENV 50204
EN 55024
Michael J. Fahrion, Director of Engineering
Document No. 485PTBR4500 - pg. 2/2
1996 B&B Electronics -- Revised November 2000
This product designed and manufactured in USA of domestic and imported parts by
Figure 2. PC Board Layout - Bottom
Figure 1. PC Board Layout - Top
Table 1
COMPONENT REPLACEMENTS FOR
CHANGING BAUD RATE TIMEOUTS
Baud
Rate
Time
(ms)
Resistor
(R3)
(ohm)
Capacitor
(C7)
(mfd)
300
33.3
330K
0.1
600
16.6
160K
0.1
1200
8.33
820K
0.01
2400
4.16
430K
0.01
4800
2.08
200K
0.01
9600
1.04
100K
0.01
19200
.520
56K
0.01
38400
.260
27K
0.01
57600
.176
16K
0.01
115200
.0868
8.2K
0.01
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