Programmable controller with multiple priority level task processing

A programmable controller for operating a machine to carry out a plurality of programmed functions, comprising:

• a memory means for storing a user defined machine control program, a user defined background task program, a first data table for storing pointers to different programs in a priority order in which the different programs will be executed, and a second data table having a plurality of storage locations for storing a pointer to an operating system routine, said memory means storing an operating system program for reversing the order in the first data table of the pointers to a machine control program and a background task program;
• a processing means for executing the user control program and the background task program thereby enabling the programmable controller to perform specific programmed functions, said processing means coupled to said means for storing to exchange program instructions and data therebetween;
• means for a user of the programmable controller to specify relative amounts of time that the processing means is to devote to executing the machine control program and the background task program, and loading a pointer to the operating system program in a specific one of the plurality of storage locations in the second data table which corresponds to a relative amount of time specified by the user;
• and
• means for sequentially accessing the storage locations of the second data table and causing said processing means to execute a program designated by a pointer stored in such storage locations, and being functionally coupled to said processing means and to said memory means.