User guide

B-1
Appendix B. Technical Details of Special
Modes of Operation
The SC932C is designed as a simple plug-in device with no internal jumpers. This Appendix
describes alternative modes of operation and also relates these to Campbell Scientific’s
original SC932 interface, for those users who are already familiar with that interface.
B.1 Power Modes
B.1.1 Normal Mode
In the normal mode of operation for the SC932C, a continuous supply of 4.3V is
available from the RTS line; this can be used as a source of power by some
interfaces, e.g. the RAD modem. The RTS and DTR lines both switch to >7V
when the SC932C becomes active. This mode will work for the majority of
applications. This mode is similar to the medium power setting of the SC932.
B.1.2 High Power Mode
A ‘high power’ setting can be forced, where RTS and DTR are held permanently
at >7V, by connecting pin 11 of the 25-way D connector to a voltage >3.5V DC.
To do this, add a link between pins 11 and 4 (RTS) on the SC932C’s 25-way D
connector. In this mode the SC932C consumes approximately 10-15mA
continuously. This mode is normally only necessary for devices which require
fully active input lines to provide a source of power to allow them to receive data
and transmit it to the SC932C.
In this mode the SC932C will not block the transmission of
synchronous data (e.g. Storage Module data) to the RS232 device.
This could cause a problem if, for example, the RS232 device is
reconfigured by the stream of binary data. Synchronous data is not
normally transmitted through the SC932C when in its normal mode
of operation.
B.1.3 Low Power Mode
The lowest power consumption can be achieved with RS232 devices which do not
need to source power from the SC932C. This is done by not connecting pin 11 or
the RTS line to the RS232 device. This is because a small current will flow from
the active RTS line into a standard RS232 RTS input on the device (normally
<1.5mA), even when the SC932C is inactive. Leaving RTS disconnected will only
work if the RS232 device does not require an active RTS line during
communication. Many high speed modems do have this requirement, by default,
but RTS/CTS handshaking can usually be turned off by software reconfiguration
(please refer to the modem manual).
NOTE