Abstract: The control program for a programmable controller is entered and edited through a program terminal which displays the control program symbolically as a ladder diagram. Comment instructions are entered into the control program and associated comment data is entered and stored. The comment data is subsequently displayed by the program terminal along with the ladder diagram rung containing the comment instruction.

Abstract: A numerical control system executes part programs which contain parameters and arithmetic expressions containing parameters. A parameter table containing parameter values is employed to evaluate parameters and arithmetic expressions during the execution of a part program, and means is provided which enables parameter values to be changed by part program instructions or manual data entry. Macroprograms, such as canned cycles, are stored in the numerical control system in a generalized form in which their instructions contain parameters and arithmetic expressions in lieu of constants. Prior to calling such a macroprogram, the part program assigns suitable values to the parameters employed in the macroprogram.