Programmable controller

A programmable controller having a trace mode, said controller comprising:

• (a) origin instruction input means for generating an origin instruction to trigger a trace function,
• (b) a memory means connected to said origin instruction input means, for receiving and storing said origin instruction,
• (c) a display means connected to said memory means,
• (d) a user program memory for storing user program instructions,
• (e) instruction execution means connected to said user program memory, for receiving and executing said user program instructions,
• (f) mode designation means, responsive to generation of said origin instruction, for designating a trace trigger mode,
• (g) instruction and trace information extraction means, responsive to a designation of said trace trigger mode, for extracting an instruction which coincides with said origin instruction from a group of instructions being subjected to execution and processing by said instruction execution means and for extracting trace information, which has a reference corresponding to said instruction extracted which coincides with said origin instruction, from a group of instructions being subjected to execution and processing by said instruction execution means, by (i) setting a first flag in the memory means responsive to a designation of said trace trigger mode, to indicate that a trace trigger function has been designated;
• (ii) extracting an instruction currently being executed from the user program memory;
• (iii) responsive to said setting of the first flag, determining whether the instruction currently being executed coincides with the origin instruction;
• (iv) if no coincidence is determined in (iii), (a) storing the instruction currently being executed in a predetermined area of the memory means, (b) completing execution of this instruction, and (c) repeating (i), (ii) and (iii);
• (v) if a coincidence exists between the instruciton currenty being executed and the origin instruction, (a) setting a second flag in the memory means to prevent (iii) from being performed again until the trace trigger function has been terminated, (b) storing the instruction currently being executed in a predetermined area of the memory means, and (c) completing execution of this instruction, and (vi) sequentially extracting successive instructions for current execution from the user program memory and sforing said successive instructions in predetermined areas of the memory means.