SHARED STORAGE DEVICE

PURPOSE:To select the word length and the constitution of read data by properly selecting a storage area by a used host device and accessing data having the set word length through a set data bus. CONSTITUTION:When a microprocessor which uses a 16-bit data bus gets the bus right, this state is reported to a memory selecting circuit 23 and a port selecting circuit 24. Further, an address signal is inputted through busses 25 and 26. The circuit 23 selects both memory elements 20a and 20b of a shared memory 20 in this case. When the same address signal is inputted to elements 20a and 20b in this state, data is outputted to an upper byte 16a and a lower byte 16b of the 16-bit data bus through switches 22a and 22b. When an I/O device which uses data having 8-bit word length gets the bus right, the circuit 23 selects the element 20a or 20b. When the address signal is inputted to the memory 20, data is outputted to a data bus 17 from one memory element of the memory 20.