While writing which shows the fact that it is in the midst of

摘要

PROBLEM TO BE SOLVED: To exchange information without lowering the reliability of information to be exchanged through a common memory by making the processing request of write request higher than that of read request. ;SOLUTION: In the common memory 13, an in-writing flag FW and a write counter which counts a writing operation frequency CN are provided and after the in-writing flag FW is set at a write request, information is written in the common memory 13; and then the in-writing flag FW is reset and the value of the write counter is updated. At a read request, information is read out of the common memory 13 only when the in-writing flag is reset; if the value of the write counter or the state of the in-writing state changes before or after the information is read out of the common memory 13, the information obtained by the reading operation is discarded and a read means is put in operation again.;COPYRIGHT: (C)1997,JPO