Vaisala WXT520 - Manual (Page 49)

Chapter 5 _______________________________________________ Wiring and Power Management
VAISALA_______________________________________________________________________ 47
Internal Wiring
The 8-pin M12 connector is wired for RS-232, SDI-12, and RS-485
modes by default. The 4-wire RS-422 requires a different internal
wiring (see also
Table 1 on page 46 ). Refer to the figure below if you
need to change the wiring of the M12 connector.
0505-205 Figure 23 Internal Wiring
The RS-232 interface can be accessed through the M12 connector using
a standard PC serial port. Same applies to the SDI-12 interface, since the
Rx and Tx lines are separate at the M12 connector.
Bidirectional use of the RS-485 and RS-422 interface requires a proper
adapter module between the PC and WXT520. For testing purposes, the
inverted output of either interface (screw terminal pin #3 TX-) is
directly readable with PC's Received Data line. In this case Signal
Ground for PC serial port is taken from screw terminal pin #6 SGND
(for testing purposes pin #19 VIN- will also do).
For configuration work, the Service Port is most practical, since it has
constant and convenient line parameters: RS-232/19200, 8, N, 1. See
Chapter 6, Connection Options, on page 55 and Figure 4 on page 21 ).
NOTE The true SDI-12 line requires that the Rx and Tx wires are joined
together (outside WXT520). See the interface diagrams in the next
section.