| 摘要 |
<p>PROBLEM TO BE SOLVED: To add a function without increasing the number of external terminals in a semiconductor device such as a combo chip or the like. SOLUTION: In a combo chip 110 in which a random-access memory(RAM) circuit 13 and a read-only memory(ROM) circuit 14 are built, a register 22 which fetches and holds the value of a data signal D0 on the basis of a register enable signal RGEB generated by a control circuit 11 is installed. The output signal of the register 22 is input to the ROM circuit 14 as the most significant bit signal A18 of an address via an address buffer 12. When a selection signal which selects both the RAM circuit 13 and the ROM circuit 14 is input to an external terminal (RAMCSB=ROMCSB='0'), the control circuit 11 sets the register enable signal RGEB at '0', and the value of the data signal D0 is fetched by the register 22. When the value is used as the most significant bit signal A18 of the address in the ROM circuit 14, the address space of the ROM circuit 14 is expanded.</p> |
