Card Setup
Line Termination
Typically, each end of the RS-485 bus must have line terminating resistors (RS- 422 terminates at the receive end only). A 120 ohm resistor is across each RS- 530/422/485 input in addition to a 1K ohm pull-up/pull-down combination that bias the receiver inputs. Headers E1 and E4 allow the user to customize this interface to their specific requirements. Each jumper position corresponds to a specific portion of the interface. If multiple OMG-ULTRA-SIOadapters are configured in a RS-485 network, only the boards on each end should have jumpers T, P & P ON. Refer to the following table for each position’s operation:
LConnects the TX+ to RX+ for RS-485 two wire operation.
T Adds or removes the 120 ohm termination.
L Connects the TX- to RX- for RS-485 two wire operation.
P Adds or removes the 1K ohm pull-down resistor in the RS-422/RS-485 receiver circuit (Receive data only).
P Adds or removes the 1K ohm pull-up resistor in the RS-422/RS- 485 receiver circuit (Receive data only).
L
T
L
P
P
Figure 10 - Headers E1 and E4, Line Termination
