Programmable controller with dynamically altered programmable real time interrupt interval

In a programmable controller which comprises:

• a memory for storing a user control program comprised of a set of control program instructions and for storing a user interrupt routine comprised of a second set of control program instructions;
• data table means for storing a real time interrupt interval number;
• main processor means coupled to the memory and the data table means for repeatedly executing the user control program to operate a machine connected to the programmable controller, said processor means including means for writing a real time interrupt interval number to the data table means when the processor means executes selected ones of the control program instructions;
• real time clock means coupled to the main processor means and the data table means, which interrupts the execution of the user control program at time intervals determined by the value of the stored real time interrupt interval number;
• wherein the main processor means executes the user interrupt routine each time the user control program is interrupted;
• and
• in which the real time clock means includes RTI in progress means for establishing the length of time required by the main processor means to execute the user interrupt routine after it is interrupted by the real time clock means, and comparison means for altering the length of time between real time interrupts from that indicated by the real time interrupt interval number when the length of time required by the main processor means to execute the user interrupt routine exceeds a preestablished portion of the interrupt interval indicated by the real time interrupt interval number.