| 摘要 |
PURPOSE:To prevent the destruction and alteration of the programs, the data, etc., as much as possible by providing a check means which checks the instruc tion codes used to a user program. CONSTITUTION:When a user program load routine is selected, the instruction and data codes of a user are inputted via an I/O terminal 1a and then sent to a check circuit 10 via a CPU 6. The circuit 10 checks whether the instruction code if confirmed is identical or not with a commanded instruction code that can be used by the user. If the data is identical with a commanded instruction code or a data code, this code is loaded in a user program area of a memory 18 and sved there. If the data is identical with an instruction code except the commanded instruction code, the circuit 10 sends the signals to a NOR circuit 12 and an inhibition circuit 14 to prevent the loading of the instruction. Then the circuit 14 inhibits the writing operations to the user program area of the memory 18 and at the same time the CPU 6 processes as the errors. |
