SEMICONDUCTOR INTEGRATED CIRCUIT

摘要

PURPOSE:To complete ROM with high density in a short delivery term by a method wherein multiple programs are contained in the system area formed in the early phase of a diffusion process while any user-specified programs are contained in the user area formed in the later phase of the same. CONSTITUTION:ROM may be classified into NAND type and NOR type and the former wherein data are written in the early phase of diffusion process requires for longer delivery term after receiving user's specifications while the latter wherein data are written in the later phase of the same can shorten the delivery term. In other words, the writting process depends upon if a transistor output is connected to data line or not and acutually almost all writting processes are performed in connecting or gate wiring process i.e. the later process in diffusion process. 0-(X-1) address is formed of NOR type ROM as program containing area 12 for user's specifications and X-Z address is formed of NAND type ROM as multipurpose program containing area 11 for system fixed high operational frequency since NOR type only requires for larger area. In such a constituion, the delivery term may be shortened subject to no remarkable increase in overall ROM area.