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SDM-SIO1A and SDM-SIO4A Serial Input/Output Modules
7.1.3 Using the RS-232 Link in Receive-Only Mode
7.2
Power Conservation
7.3
Schematic
24
To place the SDM-SIO1A into RS-232 receive-only mode, use the
SerialOpen() instruction with the SerialOpenFormat value set within the
range of 64 to 79. Consult Section 6.3.1.1, SerialOpen
information about these settings.
In receive-only mode, the SDM-SIO1A will consume less current than normal
but still can receive new information on its RS-232 port.
The example below will set the SDM-SIO1A with address 0 into receive-only
mode. All normal baud rates and buffer sizes are supported.
Example
SerialOpen (32,115200,64,100,10000)
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 datalogger
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 polled measurements, simply by closing the serial port,
using SerialClose() (see Section 6.3.1.2, SerialClose
RS-232 mode with a sensor that only sends data one way to the datalogger, run
the SDM-SIO1A in "receive-only mode" as this does not turn on the output
drivers (see Section 7.1.3, Using the RS-232 Link in Receive-Only Mode
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 datalogger has not. It does, however, mean that
the SDM-SIO1A does not start up in its lowest power mode. To place the
SDM-SIO1A into its lowest power mode, you will need to run the
SerialClose() instruction.
FIGURE
7-1
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.
, for more detailed
(p. 16)
'Set receive only mode
). When running in
(p. 19)
(p. 24)
).
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