| 摘要 |
PURPOSE: To provide a computer system that can fit different boot ROM elements without increasing the number of terminals of a semiconductor device, even while lowering costs and ensuring sufficient logic quality. CONSTITUTION: In the system, there is provided a selecting means for selecting either one of an internal timing signal supplied from the inside of a system or an external timing signal supplied from the outside of the system, as a read- out timing signal for an external memory storage storing instructions, which are executed initially after a power supply is started up. A decision means is arranged which determines whether the external timing signal value varies within a predetermined time, during resetting of the computer system or after the resetting. The selecting means selects the external timing signal when the external timing signal value has varied, and selects the internal timing signal when the external timing signal value does not vary within the predetermined time.
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