User Manual

6 USB-2-485 Interface Converter
Trinamic Motion Control GmbH & Co KG
Sternstraße 67
D – 20357 Hamburg, Germany
Phone [phone] - 0
FAX: [phone] - 60
http://www.trinamic.com
In order to support multiple-masters, the transmitter of the USB-2-485 is switched off as long as there is no
transmission going on. This may lead to an undefined level on the bus in case there is no active transceiver.
Therefore, in addition to the 120 Ohm termination resistor, the USB-2-485 includes an additional 1k Ohm resistor
from RS485+ (RS485A) to +5V and another 1k Ohm resistor from RS485- (RS485B) to GND (Figure 2). This will
always ensure a valid and stable level on the bus. In contrast to the termination resistor, there is no need to add
these two resistors also at the other end of the bus. If one of these resistors is not required / desired, they may be
removed (pleas find the location of the resistors in Figure 2).
Figure 2: Internal resistor network connected to RS485 interface and location of resistors (pcb top view)
With the USB-2-485 there is no local loopback. That is, the RS485 receiver is switched off as long as the RS485
transmitter is active.
15
69
RS485- (RS485B)
RS485+ (RS485A)
GND
USB_+5V
R1
120
R2
1k
R3
1k
RxD
TxD
USB_GND
USB-2-485
R3
1k
R2
1k
R1
120