Red Lion LEGEND - Manual (Page 40)

TROUBLESHOOTING SERIAL COMMUNICATIONS
If problems are encountered when interfacing the Legend(s) and host
device or printer, the following check list can be used to help find a solution.
1. Check all wiring. Refer to the previous application examples and use them
as a guide to check your serial communication wiring. Proper polarity of all
Legend(s) and other peripherals must be observed.
2. If the Legend is connected to a “host computer”, device or printer, check to
make sure that the computer or device is configured with the same
communication format as the Legend. The communication format the
Legend will accept is; 1 start bit, 7 data bits, no parity or 1 parity bit (odd or
even), and 1 stop bit.
3. Check the baud rate and parity in the Program Communication Module and
make sure all devices on the line are set to the same baud rate and parity.
4. Check the Legend’s unit address. If the Address command is not used when
transmitting a command to the Legend, the Legend’s address must be set to
0. See “Sending Commands & Data” section for command structure.
5. If two way communications are to be established between the Legend and a
computer, have the computer receive transmissions from the Legend first.
Activating a User Input, programmed for the print request function, will
initiate transmissions from the Legend.
6. When sending commands to the Legend, an asterisk * (2Ah) must terminate
the command. NO CARRIAGE RETURNS (0Dh) OR LINE FEED (0Ah)
CHARACTERS SHOULD BE SENT TO THE LEGEND. If they are sent,
the Legend will respond by transmitting an “E”.
7. In multiple unit configurations, make sure each unit has a different address
other than zero. If a transmit value or Print Request command is issued, an
asterisk (*) must be sent before sending another transmission.
8. If all of the above has been done, try reversing the polarity of the
transceiver wires between the Legend(s) and the RS485 interface card.
Some cards have the polarity reversed.
9. A twisted pair with a signal ground may be needed in some applications to
establish a ground reference. The signal ground is required if the
equipment does not have internal bias resistors connected to the RS485
transceiver lines. The signal ground is connected from only one Legend to
the RS485 equipment.
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