COMPATIBILITY OVERVIEW

The CTI 2500 Series® Processor is designed to be compatible with customer applications 

that use the Simatic® 545 and 555 controllers. While the CTI 2500 matches or exceeds

the capabilities of these processors in most aspects, there are a few areas in which the

CTI 2500 operates differently.

Relay Ladder Logic

The RLL used in the controller provides equivalent instructions for all Simatic® 555

instructions except the XSUB instruction. External subroutines are not supported.

If you download a program containing the XSUB instruction, it will be ignored.

In many cases XSUB is used for communications with Siemens® Profibus HMI panels.

For these installations we have a CTI program free on our website which replaces the XSUB.

For XSUB uses other than Siemens® HMI panels, CTI and our partners can develop XSUB

replacement software using SF programming. Please contact us.