USB-2-485
Interface
Converter
5
2.2.2 RS485
The 2-wire RS485 half-duplex interface of the USB-2-485 device supports all common data rates up to 3Mbit/s.
The two differential signals are available on pin 2 and pin 7 of the 9-pin D-SUB connector of the USB-2-485 device
(table 2).
Pin
Function
1
2 RS485-
(RS485B)
3 GND
4
5
6
7 RS485+
(RS485A)
8
1 2 3 4 5
6 7 8 9
9
Table 2: RS485 9-pin D-SUB male connector, pin assignment
RS485 is a multi-master bus with one master being active at a time. According to ISO8482 up-to 32 masters are
supported and line lengths of up-to 500m. With current transceiver technology even more than these 32 devices
are possible. For proper operation with longer wires, line termination at both ends of the bus is required. One
termination resistor (120 Ohm) is already included with the USB-2-485 device for easier set-up. Please add another
120 Ohm termination resistor at the other end of the bus (Figure 2).
Figure 2: RS485 interface, external bus connection with termination resistor
1
5
6
9
RS485- (RS485B)
RS485+ (RS485A)
GND
120
