Vaisala HMP240 - Manual (Page 102)

HMP240
Appendix 2: RS 485/422 serial port module
M210300en
100
4.2 POLL mode
If a transmitter has been set to POLL mode, it will respond only to commands
sent with its address:
send 22
RH= 24.4 %RH T= 29.1 'C
Addresses from 1 to 99 can be used. According to the RS 485/422 standard a
maximum of 32 devices can be connected on same bus, but the number can be
increased if the line length and/or baud rate is reduced.
More than one baud rate can be used on an RS 485 line. E.g. the host of the
line can use different baud rates with different devices (this makes it possible
to use the same address for several devices).
The line terminations must be dynamic; e.g. an RC circuit is used instead of a
simple resistor termination. Each RS 485 module has a dynamic line termina-
tion so it can be used at the end of a line.
4.3 RS 485 network settings
HMP240 settings Single pair Dual pair
Full duplex/half duplex HDX FDX
Echo on/off OFF ON
Terminal settings Single pair Dual pair
Line feed after carriage re-
turn yes no
HDX/FDX FDX FDX
When terminal is set to general <lf> (line feed) after <cr> (carriage return),
the listings will have two line feeds where also the HMP240 transmitters send
line feed.