User Guide
9
It is advisable to check the difference in ground potential with some caution before
connecting any wires, to ensure the potential differences are reasonably close and
excessive current will not flow between the two ground wires. There is a current
limiting resistor fitted in the 0V line in the SDM-SIO1, but this will not be
adequate in the event of a serious ground fault, e.g. the ground references being
240 V apart, due to faulty AC wiring. If a large potential difference is found
please seek the advice of a qualified electrician before continuing with the
installation.
3.3 Examples for connecting the SDM-SIO1 to other equipment
3.3.1 RS-485 one to one connection example
Notes:
Z, Y, B and A are connected to their corresponding differential wire pairs
when in RS-485/RS422 mode. Where A and Y are the ‘+’ lines and B
and Z are the ‘-‘ lines.
Connections 7-10 are connected internally to connections 12-15. This
allows for terminations resistors to be added when in RS-485 mode (if
needed) or, more than one connection to the I/O lines or TX and RX lines
in RS-232 mode.
If the use of termination resistors is required in RS-485 mode then they
should be connected between pins TX-Z and RTS-Y for the ZY line and
CTS-B and RX-A for the A B line (see diagrams elsewhere in document).
In half duplex RS-485/RS-422 mode the Z Y and A B pairs are connected
internally by the hardware without the need for any user interaction. The
user should connect their wires to ZX and YS, as ‘A’ and ‘B’ are
disabled.
C1
C2
C3
G
+12V
G
RX - A
CTS - B
RTS - Y
TX - Z
0V
Z
Y
B
A
RS-485 0V
RS-485_Z
RS-485_Y
RS-485_B
RS-485_A
R
R
To logger
RS-485
485
equipment
with
termination
n
resistors
100R or higher
1
2
3
4
5
6
7
8
9
10
- Z
11
12
13
14
15
