Applies To:
  • CitectSCADA 5.xx, 6.00
  • CitectHMI 5.xx, 6.00

I have configured an I/O device using the UNITE protocol as per the online help. But when I start up Citect, I get #COM on the page, and in the Kernel or Syslog.dat file, I see the following error:

UINT 0008 Port1_Board1 IODev 16

Generic 000008 Driver 00000257 (0x00000101)

And the Hardware Alarm:

06:56:26 PM IODev PLC Server I/O Device off-line, cannot talk 101 PLC is busy

I can ping the PLC, and I am sure my Citect configuration is correct. How do I fix this error?


The solution to this problem in this particular case was the XWAY address had not been configured in the PLC. The XWAY configuration is different for the TSX Premium (PL7 programming software) to the TSX Premium (Unity programming software). Be sure to consult the programming software and PLC manual for details on configuring the XWAY address.

Once the XWAY address was configured, and downloaded to the PLC, Citect could communicate without any problems.

The error message "PLC is busy" is misleading, but basically means that the PLC recieved the response, but in this case could not service the requested XWAY address since it didn't exist, so sent a PLC is busy error message.

Another reason why you might get "PLC is busy" is the Address in the I/O Device Form is incorrectly configured to what the actual XWAY address on the PLC is.

There was also one circumstance where this error message intermittently came up, and it was attributed to the PLC not having enough resources to handle the communication request. This can sometimes happen since an ETY (Premium Ethernet Module) can only handle 4 connections at a given time.

It is recommended that you have a dedicated ETY module purely for SCADA communications if you experience this problem due to communication overloading.

Quick Setup Guide for UNITE in Citect:

Run Communications wizard, select External I/O Device, then select the Manufacturer: Telemecanique, Model:TSX Premium & Micro, Communications: Ethernet (TCP/IP). Enter the IP Address of the ETY module. Leave the Port number as 0. And leave the protocol as TCP. Click next, until you finish the wizard.

Now open the Communications, I/O Device form, and enter the XWAY address of the PLC in the address field. For instance, if you have configured the PLC with XWAY address 1.10, you should enter the address as 1.10.0.

The last number in the address is the Gateway address, which defaults to 0, unless you are dropping off the rack onto FIPWAY, or UNITELWAY etc...

By default, Citect's XWAY address is as follows:


You can chose to manually enter these details in the Citect.ini file, but if you don't, the above settings will be used. Please note that the XWAY Network number of the PLC must match the XWAY Network number configured for Citect. CitectSCADA, PL7 Programming Software and the PLC must each have a unique Station number. If there is a Station number clash, you will most likely see a Generic error 7, Driver error 0x15 in Citect.

The final step is to Compile the project and run the computer setup wizard.