Campbell Scientific SC932C Interface - Manual (Page 9)

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-pin 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-pin 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.
NOTE: 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).
B.2 HANDSHAKING LINES
In its normal power mode, and when inactive
(i.e., the datalogger ME line is low) the SC932C
only holds the RTS line high to provide a source
of power to line-powered modems, such as the
RAD modem.
The DTR line is controlled by the ME line of the
datalogger. When ME is high the DTR line is
powered high (>7V), but when the ME line
returns to a low state, the DTR line enters a
high impedance state; as far as the RS232
device is concerned, this has the same effect as
the DTR line going low. This transition can be
used to force the device to go off-line, if the
device supports this.
This feature is useful for some telephone
modems as it allows the datalogger to force the
modem off-line. The older SC932 only supports
this type of handshaking when operated in its
low power mode.
NOTE: The SC932C can be modified to
support a form of RTS handshaking for the
support of some specialized half-duplex
interfaces. Please contact Campbell
Scientific for further details.
B.3 ‘PRINTER ONLY’ OUTPUT
The SC932C can be used as a printer (PE/SDE
enabled) device. However, unlike the SC932
where this mode can be set using internal
jumpers, the SC932C requires a special
connection in place of the normal direct SC12
cable. The connection to the SC932C should
be made up as follows: