Quatech QSU-300 Manuale Utente

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RS-422/485 signal description 

DB-9 

Auxiliary Input (AuxIn–) 

9 

Configuring termination resistors 

Factory installed resistors allow for Freedom USB-200/300 signal line 

termination in compliance with RS-422 and RS-485 standards. You 

can select or remove the desired termination by configuring the 
associated jumper for each port. The following Figure shows the 

factory default configuration: no termination. 

Figure 41 - RS-422/485 jumper settings 

2
1

4
3

2
1

4
3

Factory Default = pins  3 & 4

(no termination)

J3

J2

CN1

 

Jumpers J2 through J5 (DSU) or J2 through J9 (QSU/ESU/HSU) 
allow the following selections: 

RS-422 (100 ohm) termination 

 

 

 

 

 

RS-485 (120 ohm) termination 
no termination 

For normal operations over shorter distances or when using a 

termination in the connecting cable, use the default setting. For 
communications over great distances or if termination via the 

connecting cable is not feasible, configure the jumpers for the desired 

termination as follows. 

RS-422 termination, jumper pins 1 and 3 
RS-485 termination, jumper pins 2 and 4 

Only terminate signals that are present in the cable. If the auxiliary 

input is not used and is not needed or wired in the cable, do not select 

the auxiliary input termination on the board.  See the following Table 
for termination jumper assignments. 

Configure each DB-9 connector as shown in the Table below. 

Table 5 - RS-422/485 termination jumpers