SECTION 6. 9-PIN SERIAL INPUT/OUTPUT

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 CR10 is connected to the SC32A RS232 interface and a modem/terminal, and an "*" is not received after sending carriage returns:

1.Verify that the CR10 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 6.7-2). 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.

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 with Table 6.7-2.

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.

Campbell Scientific's TERM program (part of the PC208 Datalogger Support Software) provides this function for IBM PC/XT/AT/PS-2's and compatibles. The port should be enabled for 300, 1200, or 9600 baud, 8 data bits, 1 stop bit, and no parity.

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).

IF GARBAGE APPEARS

If garbage characters appear on the display, check that the baud rate is supported by the CR10. If the baud rate is correct, verify that the computer/terminal is set for 8 data bits, and no parity. Garbage will appear if 7 data bits and no parity are used. If the computer/terminal is set to 8 data bits and even or odd parity, communication cannot be established.

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