Vaisala HMP260 - Manual (Page 92)

HMP260 SERIES
HMP260-U017en-1.5 Appendix 3: RS 485/422 serial port module
2 OPERATION
The HMP260 transmitters can either be given an address or operated without
an address. Both single and dual loop wiring with half duplex connection can
be used. No address is needed when only one HMP260 transmitter is used;
when several transmitters are connected to the same line, each transmitter
must be given an address in the initial configuration.
A single transmitter can get its operating voltage from the master or it can
have its own (floating) power supply or it has the power supply module in
use.
The serial line structure is a parallel interfaced chain (daisy chain). At the
ends of the serial line there must be a HMP260 transmitter, dynamic line
adapter (120 ohm resistor in series with a 33 nF capacitor) or line master. If a
branch line is made with a junction box, the branch should be shorter than 3
meters.
When connecting the device, follow the instructions given in the figure in
Chapter 1.
TX HI
TX L O
TWISTED PAIR WIRING
-
HOST COMPUTER
DUAL LOOP WIRING
TWISTED PAIR WIRING
HOST COMPUTER
RX L O
RX HI
TX HI
TX LO
RX LO
RX HI
TX HI
TX LO
RX L O
RX HI
TX HI
TX LO
R X LO
R X HI
TX HI
TX LO
RX LO
RX HI
120R
33 nF
TX HI
TX L O
RX LO
RX HI
120R
33 nF
120R
33 nF
NOTE: DYNAMIC LINE TERMINATION
REQUIRED IF NO DEVICE
AT THE END OF THE BUS.
NOTE: DYNAMIC LINE TERMINATION
REQUIRED IF NO DEVICE
AT THE END OF THE BUS.
HMP260 transmitters
1 to n pieces
HMP260 transmitters
1 to n pieces
SINGLE LOOP WIRING