| 摘要 |
PURPOSE:To protect the software stored internally, by providing a readout control memory in a microcomputer, writing a readout inhibiting signal after debugging, and inhibiting the output operation of a bidirectional bus control circuit with the output of readout control memory. CONSTITUTION:After data are written and verified in an ROM2 of a microcomputer 1, readout is inhibited externally to the data of the ROM2. In supplying a pulse overvoltage signal of ''H'' to an input terminal I1 and writing ''H'' to a specific bit of a readout control memory 7, this output is normally ''H'' and the output of an OR gate 8 keeps ''H'' to be outputted at all times independently of the readout signal applied to an input terminal I2. Thus, the data output operation of a bidirectional bus control circuit 6 is inhibited. Then, the readout of the software data written in the ROM can be prevented and the software is protected. |
