| 摘要 |
PURPOSE:To prevent data from being destroyed due to write on a PROM simultaneously with the readout prohibition of PROM data by prohibiting the readout of the data written on the PROM by using a PROM mode permission/prohibition discrimination circuit. CONSTITUTION:The PROM mode permission/prohibition discrimination circuit 8 which inputs the output of a PROM mode detection circuit 5 so as not to set a PROM mode and outputs a control signal to a state selection circuit 6 and an input/output port B7 is added as a means to prohibit the readout of the data in a PROM part 1. When the readout of the data in the PROM part 1 is prohibited, the PROM mode permission/prohibition discrimination circuit 8 outputs a signal to prohibit the PROM mode to the state selection circuit 6 and the input/output port B7 in spite of the output signal of the PROM mode detection circuit 5. Thereby, it is possible to prevent the data from being destroyed due to the write on the PROM simultaneously with the readout prohibi tion of the PROM data. |
