Grid Connect Revision A, 6/2/11
BF-850
USB/RS-485/RS-422 Converter
User’s Manual
1.0 General introduction
In a fast developing PC industry, the USB interface is
replacing many old PC serial interfaces one step at a time.
However, many types of important equipment still use
RS-422/RS-485 interfaces in order to transfer data. This is why
there is need for the USB/RS-422/485 converter.
The BF-850 is a commonly used type of converter. It is
powered from the USB interface of a PC and does not need any
external power source. It also conforms to the USB, RS-422 and
RS-485 standards. There is no delay and the signal is converted
automatically inside the device. The unique I/O auto-controls
the direction of data transfer, and needs no handshake signals (like
RTS or DTR) to transfer with full duplex (RS-422) and half
duplex (RS-485).
The BF-850 can provide a reliable connection with point to
point and point to multi-point data transfer. In point to multi-point,
each converter can connect up to 32 units of RS-422 or RS-485
interface. The speed of data transfer is between 300 and 921600
bps and the communication types are USB to RS-422 or USB to
RS-485.
2.0 Performance parameter
1. Standard
：
Conform to the standards of USB V1.1, EIA RS-485, and
RS-422.
2. USB signal
：
VCC, DATA+, DATA-, GND, FG
3. RS-485 signal
：
T+, T-, GND
4. RS-422 signal
：
T+, T-, R+, R-, GND
5. Communication type
：
Asynchronous communication, point to point or point to
multi-point, 2 lines of halt-duplex, and 4 lines of
full-duplex.
6. Communication control
：
Uses auto-control technology to transfer data and
automatically determines and controls the direction of data
transfer.
7. Baud Rate
：
300~921600 bps, automatic detect the serial port speed.
8. Load ability
：
In point to multi-points each converter can connects 32
units of RS-422 or RS-485 interface equipment.
9. Communication distance
：
RS-422/RS-485 5000 meter (9600 bps), USB less than 5
meter
10. Type of communication line
：
Double twist line or cover line.
11. Communication speed
：
921600 bps 300 M 38400 bps 2.4 KM 9600 bps 5 KM
12. Dimension
：
55mm × 36mm × 18mm
13. Operation environment
：
-25 ~ 70
℃℃
, humidity 5% ~ 95%
14. Operating Systems
Windows95/98/2000/XP/Vista/7
3.0 Connector and signal
RS-422/RS-485 export signal
DB9 PINS
Output
RS-422
Duplex
RS-485 Half
Duplex
1
T/R+
Transfer(A+)
RS-485(A+)
2
T/R-
Transfer(B-)
RS-485(B-)
3
RXD+
Receive(A+)
Empty
4
RXD-
Receive(B-)
Empty
5
GND
Ground
Ground
6
N/A
7
N/A
8
N/A
9
N/A
4.0 Installation setup and application
The BF-850 uses a USB/DB-9 connector and needs no
crossover cable. T/R+ and T/R- represent transfer and
RXD+/RXD- represent receive. GND represents the public
ground line.
The BF-850 provides 4 types of communication as below
：
1. Point to point/4 lines full-duplex
2. Point to multi-point/4 lines full-duplex
3. Point to point/2 lines half-duplex
4. Point to multi-point/2 lines full-duplex
Half-duplex (RS-485)
Connect the 2 lines to T/R+ and T/R-
Full-duplex (RS-422)
Connect the 4 lines to T/R+, T/R-, RXD+ and RXD-
When connecting full-duplex or half-duplex, in order to
prevent reflection or interference of the signal, you need to
connect a resistance at the end of line (120
Ω
1/4W).
