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SDM-SIO1A and SDM-SIO4A Serial Input/Output Modules
The port connections RG, G, RTS/TD+, Tx/TD–, Rx/RD+, and CTS/RD– are
labelled exactly the same for each port and match those of the SDM-SIO1A
(see TABLE 6-3).
In the examples below, the SDM-SIO4A is wired identically for the datalogger
and the serial devices.
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.
The connection of the wires to the remote serial device will vary with type of
device and method of communication. It is necessary to work out the best
mode of operation of the serial device, taking into consideration issues such as
power consumption, cable lengths (RS-485 being better than RS-232 for long
cables), synchronization of data collection, etc.
NOTE
If possible, use screened cable for connecting the SDM-SIO1A to
remote sensors or devices. Check the manual of the device for
details on where to connect the screen for maximum effectiveness.
RS-422 mode is functionally the same as RS-485 mode except the connection
is limited to a point-to-point system. Connections and programming for
RS-422 are otherwise identical to full-duplex RS-485.
When operating in RS-232 mode, the SDM-SIO1A also supports hardware
handshaking.
Section 6.2.1, Wiring Examples for Connecting the SDM-SIO1A
, provides
(p. 11)
examples of different connection schemes for the serial devices. Further
discussion of different modes of operation is given in Section 7, Operation
.
(p. 23)
6.2.1 Wiring Examples for Connecting the SDM-SIO1A
The exact method of wiring the SDM-SIO1A varies with the type of device it
is going to exchange data with. The variables include the type of interface used
(RS-232, RS-485, or RS-422), whether handshaking is used, whether the
connection is full or half duplex, and whether termination resistors are used
(RS-485 and RS-422 only).
Typical wiring for the most common configurations are given as examples in
the following subsections.
11
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