5.4.3 C terminals for communications
C terminals are configurable for the following communications types:
l
SDI-12
l
RS-232 (0 to 5 V)
Some communications types require more than one terminal, and some are only available on
specific terminals. See Communications specifications(p. 249) for more information.
5.4.3.1 SDI-12 ports
SDI-12 is a 1200 baud protocol that supports many smart sensors. C1 and C2 can each be
configured as an SDI-12 communications port. Maximum cable lengths depend on the number
of sensors connected, the type of cable used, and the environment of the application. Refer to
the sensor manual for guidance.
For more information, see SDI-12 communications(p. 137).
See also Communications specifications(p. 249).
5.4.4 RS-232 Port
RS-232 represents a loose standard defining how two computing devices can communicate with
each other. For instruction on setting up RS-232 communications with a computer, see USB or
RS-232 communications(p. 21).
One nine-pin DCE port, labeled RS-232, normally is used to communicate with a computer
running data logger support software, to connect a modem, or to read a smart sensor. The
RS-232 port functions as either a DCE or DTE device. The most common use of the RS-232 port is
as a connection to a computer DTE device (using a standard DB9-to-DB9 cable). Pins 1, 4, 6, and
9 function differently than a standard DCE device to accommodate a connection to a modem or
other DCE device via a null modem cable. For the RS-232 port to function as a DTE device, a null
modem adapter is required.
RS-232 communications normally operate well up to a transmission cable capacitance of 2500
picofarads, or approximately 50 feet of commonly available serial cable.
5.4.4.1 RS-232 Power States
Under normal operation, the RS-232 port is powered down waiting for input. Upon receiving
input, there is a 40-second software timeout before shutting down. The 40-second timeout is
5. Wiring panel and terminal functions15
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