Vaisala PTB330 - Manual (Page 46)

USER'S GUIDE____________________________________________________________________
44 __________________________________________________________________ M210855EN-D
NOTE If you use the internal termination of the barometer at the end of the
RS-485 bus (instead of using separate terminators) removing that
barometer may block the bus operation.
Table 5 Connecting the Twisted Pair Wires to the Screw
Terminals
Screw terminal Data line (2-wire RS-485) Data line
(4-wire RS-485/422)
1 (not connected) RxD0-
2 (not connected) RxD1+
3 Shield/Common Wire Shield/Common Wire
4 D0- TxD0-
5 D1+ TxD1+
Stub
Termination Termination
Termination Termination
Junction box
Junction box
Junction box
Twisted pair
120R
120R
120R
120R
Twisted pair
Stub
Stub
Baud > 19.2K Stub < 10ft, 3m
Baud > 112K Stub < 1ft, 0.3m
Rx D0-
Rx D1+
Common
Tx D0-
Tx D1+
Switch
Term off
Term off
2/4 wire on
RS422 off Tx D0-
Tx D1+
Common
Rx D0-
Rx D1+
Switch
Term off
Term off
2/4 wire on
RS422 off Tx D0-
Tx D1+
Common
Rx D0-
Rx D1+
5
4
3
2
1
RS485-1
RS485-1
Address MM
Address NN
RS485 bus master
5
4
3
2
1
1102-028
Figure 26 4-Wire RS-485 Bus