| 摘要 |
PURPOSE:To prevent data in a common memory from being destroyed owing to a runaway of a program, a fault of a CPU, etc., by providing a status discriminating circuit, a protection discriminating circuit, etc. CONSTITUTION:A boundary setting register 15 indicating boundaries between special area 17-19 and a common area 20 in common memories 6 and 7, a protection register 14 indicating whether access to the respective special areas and the common area is enabled or not, a status discriminating circuit 13 which compares statuses of CPUs 1-3 with those of the common memories 6 and 7, and a protection discriminating circuit 16 which discriminates whether access from the CPUs 1-3 is enabled on the basis of the outputs of the registers 15 and 14, and circuit 13 are provided. Access from the CPUs 1-3 to the common memories 6 and 7, only when the last statuses coincide and it is access to previously indicated area, is permitted. |
