| 摘要 |
PROBLEM TO BE SOLVED: To prevent a method for setting a test mode outputting a ROM code from being detected by a third party by providing a test mode setting circuit with first and second detection means detecting whether the pulse width of input signal from an external terminal is contained in a range preliminarily set, and first and second storing means storing it. SOLUTION: A signal to be applied to an external terminal 101 is input to an AND gate 102. To a pulse width detection circuit 103 an output signal of the AND gate 102 is input, and only when the high level width W1 of the signal satisfies a relation of D1<=W1 (D1+Δ1) a high level pulse of 1 shot is output therefrom. A flip-flop circuit of a NOR stages 105, 106 and an inverter 107 is high when a signal 104 is high pulse, while low when a reset signal is high pulse. Similarly, to a pulse width detection circuit 114 an output signal of an AND gate 113 is input, and only when the high level width W2 of the signal satisfies a relation of 2<=W2<(D2+Δ2) a high pulse of 1 shot is output therefrom. This is used as a test mode signal 116 accordingly. |
