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TABLE 6-3. SDM-SIO1A Functional Description of the Connections
Pin
Case Text
Connection To
1
12V
2
G
3
C1
Datalogger
4
C2
5
C3
6
RG
1
7
G
2
8
RTS/TD+
Equipment
9
Tx/TD–
10
Rx/RD+
11
CTS/RD–
TABLE 6-2. SDM-SIO1A Terminal Labels and Functions
Power
SDM
1
2
3
4
Power supply 0V (same as other G pin)
RG – RS-485 ground. Connected to G via 100 Ω 1 W resistor.
RS-232 RTS. RS-485 half duplex non-inverting.
RS-232 transmit. RS-485 half duplex inverting.
RS-232 receive. RS-485 receiver non-inverting.
RS-232 CTS. RS-485 receiver inverting.
1
Connection RG (pin 6) has a 100 Ω resistor in series with the datalogger ground
connection. This connection should be used when connecting RS-485 equipment by
long wire lengths. It ensures both systems have a common ground reference point. See
Section 2, Precautions
, before connecting.
(p. 1)
The G (pin 7) can be used for the RS-232 zero volt reference or any other ground
2
connection needed, for example, shields.
As shown above in TABLE 6-3, connections 1 to 5 need to be made to the
datalogger, either connecting the SDM lines to the matching control ports or
the dedicated SDM port available on some dataloggers, such as the CR3000.
When connecting multiple SDM devices to a datalogger, the SDM connections
can either be all connected by separate wires back to the datalogger terminals
or, as is common if the SDM devices are mounted in a row in an enclosure,
jumper wires can be used to daisy-chain the same terminals on each interface
together (including power and ground) with one set of wires running back to
the datalogger. It is important to keep the total length of SDM wiring as short
as possible.
SDM-SIO1A Serial Input/Output Module
Communications Connections
5
6
7
8
Description
Power supply +12V
SDM data enable line
SDM clock line
SDM data line
0V – (same as other G pin)
RS-485 full duplex outgoing.
RS-485 full duplex outgoing.
RS-485 full duplex incoming.
RS-485 full duplex incoming.
9
10
11
9
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