Connecting To A Host Terminal
Six TCU units are used to control a process in a plant. The TCU units are
located at the proper location to optimize the process. A communication line
is run to an industrial computer located in the p roduction office. Figure 26,
Connecting To A Host Terminal, shows the line connection. Each TCU is
programmedfor adifferentaddress andall areprogrammedfor thesamebaud
rate andparity asthe computer.An applicationp rogramis written tosend and
receive data f rom the units using the proper commands.
Troubleshooting Serial Communications
If problems are encountered when interfacing the TCU(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
asa guidetocheckyour serialcommunicationwiring.Properpolarity ofall
units and other peripherals must be observed.
2. If the TCU is connected to a host computer, device or printer, make sure
that the computer or device is configured with the same baud rate and
communication format as the TCU. The communication format the TCU
accepts is; 1 start bit,7 data bits, no parity or 1 paritybit (odd or even), and
1stopbit.
3. Check the TCU’s unit address. If the Address command is not used when
transmitting a command to the TCU, the TCU’s address must be set to 0.
See Sending Commands & Data, page 48, for command structure.
4. If two-way communications are to be established between the TCU and a
computer, the computer must receive a transmission f rom the TCU f irst.
Activating the User Input, programmed for the print request function,
initiates transmissions from the TCU.
5. Whensending commandsto the TCU,an asterisk (2Ah) must terminatethe
command.After systempower-upan asteriskmustbe sentto cleartheTCU
input buffer.
6. In multiple unit configurations, each unit must have a different address
other than zero.
7. If all of the above has been done, try reversing the polarity of the
transceiver wires between the TCU(s) and the RS485 interface card. Some
cards have the polarity reversed.
Figure 26, Connecting To A Host Terminal
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