Applies To:
  • CitectSCADA 5.xx, 6.XX, 7.00
  • CitectHMI 5.xx, 6.XX, 7.00

At startup a hardware alarm is triggered "Channel offline cannot talk". In the Syslog.dat file it was found that the error was Generic 8 Driver 8200 (0x2008). The error 0x2008 for the S7NT driver is "ILLEGAL REAL VALUE". 

The error could be coming due to an invalid float value stored in the register of the PLC because the driver does a float check. This float check can be disabled by using the citect.ini parameter


Refer to the knowledge base article Q3848 that explains the above.

If the float value is stored correctly in the register of the PLC and you don't want to use the above parameter then the other problem could be by reading a REAL in a block containing other data types such as INTs. The driver retrieves the data as a block. This is better explained in the S7 driver help under the section S7 Driver - Advanced Configuration and Maintenance - Potential Problems with Blocking. You can also refer to the knowledge base articles Q3901 and Q3634 regarding blocking.

Normally if you have incorrect alignment in a block then you would get a compile error because the citect.ini parameter is set to 1 by default


If this parameter is set to 0 then it must be set to 1 so that when you compile the project you can identify all the bad tags i.e. tags that would cause problems in a block that is retrieved by the driver. There are two ways of solving this problem and that is:

1. Realign the bad tags in the PLC
2. Create another I/O Device in the CitectSCADA project and move the bad tags to this newly defined I/O device. Note that if a new I/O Device is created in CitectSCADA then a new device must also be created in the Simatic Software that references to this newly created I/O Device in the CitectSCADA project.

S7NT, Hardware Alarm, Cannot Talk