| 摘要 |
<p>PURPOSE:To improve the security of a system program, etc., by making a trap request signal to a CPU significant when an operational code is fetched from an external memory area at the time of a memory expansion mode operation. CONSTITUTION:A fetch detecting means 7 is provided to generate the trap request signal when the operational code is fetched from the external memory area while the single chip microcomputer is operated in a memory expansion mode. When the operational code is fetched from the external memory area, in the memory expansion mode, the fetch detecting means 7 sets a jump destination vector at the time of trap to a built-in ROM area by sending the trap request signal for requesting the generation of forced trap interruption not to be masked by the program so that a user can limit the program at the time of trap generation, and a ROM 2 can be prevented from being illegally read out.</p> |
