Campbell CR23X, Operator'S Manual, Page: 86 / 374

SECTION 6. 9-PIN SERIAL INPUT/OUTPUT
6-8
FIGURE 6.2-5. Transmitting the ASCII Character 1
BAUD RATE
BAUD RATE is the number of bits transmitted
per second. The CR23X can communicate at
300, 1200, 4800, 9600, 19200, 38400, and
76800 baud. In the Telecommunications State,
the CR23X will set its baud rate to match the
baud rate of the computer/terminal. Some baud
rates, particularly those above 9600, may not be
supported by all CSI communications
equipment.
Typically the baud rate of the modem/computer/
terminal is set either with dip switches, or
programmed from the keyboard. The instrument's
instruction manual should explain how to set it.
DUPLEX
Full duplex means that two devices can
communicate in both directions simultaneously.
Half duplex means that the two devices must send
and receive alternately. Full duplex should always
be specified when communicating with Campbell
Scientific peripherals and modems. However,
communication between some Campbell Scientific
modems (such as the RF95 RF modem) is carried
out in a half duplex fashion. This can affect the
way commands should be sent to and received
from such a modem, especially when implemented
by computer software.
To overcome the limitations of half duplex,
some communications links expect a terminal
sending data to also write the data to the
screen. This saves the remote device having to
echo that data back. If, when communicating
with a Campbell Scientific device, characters
are displayed twice (in pairs), it is likely that the
terminal is set to half duplex rather than the
correct setting of full duplex.
IF NOTHING HAPPENS
If the CR23X is connected to the SC32A RS-
232 interface and a modem/terminal, and an "
∗
"
is not received after sending carriage returns:
1. Verify that the CR23X has power AT THE
12V AND GROUND INPUTS, and that the
cables connecting the devices are securely
connected.
2. Verify that the port of the modem/terminal is
an asynchronous serial communications
port configured as DTE (see Table 6.2-4).
The most common problems occur when
the user tries to use a parallel port, or
doesn't know the port assignments, i.e.
COM1 or COM2. IBM, and most
compatibles come with a Diagnostic disk
which can be used to identify ports, and
their assignments. If the serial port is
standard equipment, then the operators
manual should give you this information.
3. Verify that there is 5 volts between the
CR23X 5V and G terminals. Call Campbell
Scientific technical support if the voltage is
less than 4.8 volts.
Some serial ports, e.g., the Super Serial Card
for Apple computers, can be configured as DTE
or DCE with a jumper block. Pin functions must
match Table 6.2-4.
If you are using a computer to communicate
with the datalogger, communication software
must be used to enable the serial port and to
make the computer function as a terminal. The
port should be enabled for 300, 1200, or 9600
baud, 8 data bits, 1 stop bit, and no parity.
Campbell Scientific's PC208W provides this
function.
If you are not sure that your computer/terminal
is sending or receiving characters, there is a
simple way to verify it. Make sure that the
duplex is set to full. Next, take a paper clip and
connect one end to pin 2, and the other end to
pin 3 of the serial port. Each character typed on
the keyboard will be displayed only if
transmitted from the terminal on pin 2, and
received on pin 3 (if duplex is set to half, the
character will be displayed once if it is not
transmitted, or twice if it is transmitted).