| 摘要 |
PURPOSE:To prevent runaway and destruction of a program by comparing a jump destination address of a branch instruction and an address written in an area designating register with each other and inhibiting the jump to another program on a basis of the judgement of a comparing circuit. CONSTITUTION:When a branch instruction exists in an address a+h on the way of execution of a program 1, contents of the address a+h pass an area discriminating circuit 14 and are decoded as a branch instruction by an instruction decoding circuit 15, and a controller 13 sets the value of a program counter 8 to the absolute address of jump destination and inputs the value of the program counter 8 and values of area designating registers 9-12 to a comparing circuit 16, and they are compared with each other. The comparing circuit 16 discrimininates whether the value of the program counter is in the range from the start address a+h to the last address a+z of an empty area 3 or in the range from the start address a+4 to the last address a+i of the program in an area 2, and instruction in the jump destination are executed only when the value of the program counter 8 is in said range. |
