PCU10000 Datasheet, PDF (61/96 Pages) Red Lion Controls. Inc – THE PROCESS CONTROL UNIT

Connecting To A Host Terminal
Six PCU units are used to control a process in a plant. The PCU units are
located at the proper location to optimize the process. A communication line
is run to an industrial computer located in the production office. Figure 24,
Connecting To A Host Terminal, shows the line connection. Each PCU is
programmed for a different address and all are programmed for the same baud
rate and parity as the computer. An application program is written to send and
receive data from the units using the proper commands.
TROUBLESHOOTING SERIAL COMMUNICATIONS
If problems are encountered when interfacing the PCU(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
units and other peripherals must be observed.
2. If the PCU 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 PCU. The communication format the PCU
accepts is; 1 start bit, 7 data bits, no parity or 1 parity bit (odd or even), and
1 stop bit.
3. Check the PCU’s unit address. If the Address command is not used when
transmitting a command to the PCU, the PCU’s address must be set to 0.
See Sending Commands & Data, page 47, for command structure.
4. If two-way communications are to be established between the PCU and a
computer, the computer must receive a transmission from the PCU first.
Activating the User Input, programmed for the print request function,
initiates transmissions from the PCU.
5. When sending commands to the PCU, an asterisk (2Ah) must terminate the
command. After system power-up an asterisk must be sent to clear the PCU
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 PCU(s) and the RS485 interface card. Some
cards have the polarity reversed.
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Figure 24, Connecting To A Host Terminal