Sequence display controlling method and controller

A sequence program display control method for a stored-program sequence controller including memory means storing a plurality of predetermined sequence instructions for controlling a controlled-objective process in conjunction with a predetermined sequence ladder diagram including a plurality of relay contacts, said instructions including on-off commands for said relay contacts;

• input means for receiving condition signals indicative of the present state of various relay contacts of said sequence ladder diagram;
• operation control means for reading out sequence instructions stored in said memory means and for generating output control signals for said controlled-objective process in response to said sequence instructions and the condition signals provided by said input means;
• output means for outputting said output signal from said operation control means to said controlled-objective process;
• and cathode ray tube display means connected to said operation control means for displaying the conditions of operation of said sequence program, said method comprising the steps of:
• (a) storing instructions relating to a predetermined sequence ladder diagram in said memory means, said instructions for said ladder diagram being stored in an order corresponding to an array formed of a plurality of imaginary rows and a plurality of imaginary columns;
• (b) reading out the contents of said memory means relative to the first row of the diagram in a sequence successively from the first column to the last column, and repeating a similar reading operation relative to the second row to the last row successively;
• (c) inputting instructions read out in said reading step including branch information, on-off commands in the form of contact-state information and address information bits into respective bit positions of an instruction register;
• (d) decoding said inputted branch information, and inputting a control signal into a first register when said branch information indicates a branch or join to a subsequent row and inputting the same control signal into a second register when said information indicates a branch or join from the previous row, and inputting a display signal corresponding to a branch information bit pattern into an accumulator;
• (e) storing, when a branch to the subsequent row is present in the decoded branch information, the value of said accumulator in a bit position of a first-in, first-out column register corresponding to the stored bit position of said first register and thereafter shifting the content of said first register by one bit;
• (f) inputting to the accumulator, when a branch or a contact from the previous row is present in the decoded branch information, the bit content of the column register corresponding to the stored bit position of said second register and thereafter shifting the content of said second register by one bit, and
• (g) performing a logical operation on the condition signal inputted to said input means, a signal from said accumulator and a signal obtained by decoding of said contact-state information in said instruction so as to produce a display information signal to be applied to said CRT display means.