| 摘要 |
<p>A single chip microcomputer coupled to an external memory includes a latch circuit having a data input connected to an operation mode designation terminal and a toggle input connected to a reset terminal, so that a logical value of the operation mode designation terminal is latched in the latch circuit at the moment the resetting is released. An output of the latch circuit is connected to an address discriminating circuit, which also receives an address so as to discriminate whether the received address is directed to an internal ROM or an external memory so that the address discriminating circuit controls an associated selector to cause it to select the internal ROM in the former case and the external memory in the latter case or when the output of the latch circuit indicates the external memory. With this arrangement, even if the logical value of the operation mode designation terminal changes after the resetting is released, the output of the latch circuit does not change. Accordingly, when the operation was started with the external memory operation mode, the operation mode is in no way changed to the internal ROM operation mode in the course of execution of a program. Therefore, secrecy of the content of data in the internal ROM can be maintained. <IMAGE></p> |
