Omega Engineering OMG-CONV-485-ISO 사용자 설명서

 

Card Setup 

OMG-CONV-485-ISO 

Page 4 

Typically, each end of the RS-485 bus must have a line-terminating resistor 
(RS-422 terminates at the receive end only). A 120-ohm resistor is across each 
RS-422/485 input in addition to a 1K-ohm pull-up/pull-down combination that 
biases the receiver inputs. Dip switch SW2 allows customization of this interface 
to specific requirements. Each dip switch position corresponds to a specific 
portion of the interface. If multiple OMG-CONV-485-ISO adapters are configured 
in an RS-485 network, only the adapters on each end should have dip switch 
SW2 position 1 on. One adapter should have dip switch SW2 positions 2 and 3 
on. Refer to the table below for each position’s operation. 

Dip switch SW2 position 6 is used to control the RS-485 enable/disable functions 
for the receiver circuit and determines the state of the RS-422/485 driver. The RS-
485 ‘Echo’ is the result of connecting the receiver inputs to the transmitter 
outputs. Every time a character is transmitted, it is also received. This can be 
beneficial if the software can handle echoing (i.e. using received characters to 
throttle the transmitter) or it can confuse the system if the software does not. To 
enable the ‘No Echo’ mode dip switch SW2 position 6 should be on. 

 

1 

Adds or removes the 120-ohm termination 

2 

Adds or removes the 1K-ohm pull-up resistor in the RS-422/RS-485 
receiver circuit (Receive data only) 

3 

Adds or removes the 1K-ohm pull-down resistor in the RS-422/RS-485 
receiver circuit (Receive data only) 

4 

Connects TX+ to RX+ for RS-485 two-wire operation 

5 

Connects TX- to RX- for RS-485 two-wire operation 

6 

Receiver Echo Off/On (On = Echo Off)