PURPOSE: To realize a perfect loading even in case the read instruction is applied during execution of the write instruction, by producing the write priority signal via the monostable multivibrator which is triggered by the write control pulse.

CONSTITUTION: With application of the write control write clock, the monostable multivibrator 29 is triggered. The pulse of a fixed duration delivered from the multivibrator 29 is turned into the write priority signal. For the address delivered from the address multiplexer 21, the write address is selected for a fixed period without any selection of the read address. Thus the data is written by preference into the RAM11. The writing is also carried out by preference even in case the read instruction is applied under execution of the write instruction. Thus the loading is performed completely to the RAM to prevent the loss of the data.