| 摘要 |
<p>PURPOSE:To prevent the undesired transfer of the contents of an internal ROM by starting by processing by the 1st and 2nd external ROMs according to an external access signal then making the switching of the external access signal impossible, unless otherwise producing a reset signal. CONSTITUTION:When an external access signal Ea is set at ''1'', an internal ROM1 having capacity including address #0-#(a-1) is used together with an ROM2-1 outside the 1st area having capacity including addresses #a-#(b-1) and an ROM2-2 outside the 2nd area including addresses #0-#(a-1), respectively. The signal EA is selected in response only to a reset signal which starts a 1-chip microcomputer at and after the address #0. Based on the signal EA, the processing is started with use of the ROM2-2 and ROM2-1. Then the switching of the signal EA is made impossible unless otherwise the reset signal is outputted.</p> |
