Power Conservation; Schematic - Campbell SDM-SI01A Product Manual

7.2 Power conservation

The SDM-SIO1A features an industry-standard RS-232/RS-485 driver chipset to ensure maximum
likelihood of compatibility with all other devices. When the driver is powered on, it uses more
power than one of the data logger control-port-based COM ports — typically 6 mA minimum.
This is partly because it generates the correct signal levels, which in itself requires power, and
partly because, in the case of RS-232 signals, the resting state of ~ –6 V driving a nominal RS-232
~3 k load implicitly wastes ~2 mA of current per line.
To avoid excess current waste, the chip can be turned off when not in use, for example, between
SerialClose()
polled measurements, simply by closing the serial port, using (see
SerialClose() [p. 22]). When running in RS-232 mode with a sensor that only sends data one way
to the data logger, run the SDM-SIO1A in "receive-only mode" as this does not turn on the
output drivers (see Using the RS-232 link in receive-only mode [p. 25]).
If using RS-232 mode, also avoid connecting handshaking lines that are not required to avoid an
unnecessary 2 mA drain per line.
The SDM-SIO1A will start up with its last set of baud rate and protocol settings. This feature is to
protect against brownout conditions where the SDM-SIO1A has reset but the data logger has
not. It does, however, mean that the SDM-SIO1A does not start up in its lowest power mode. To
SerialClose()
place the SDM-SIO1A into its lowest power mode, you will need to run the
instruction.

7.3 Schematic

Figure 7-1 (p. 27) shows the internal configuration of the SDM-SIO1A when configured in RS-485
or RS-422 full-duplex mode. This shows the internal resistors to aid users trying to test system
interconnections and drive levels.
SDM-SIO1A and SDM-SIO4A Serial Input/Output Modules 26