| 摘要 |
<p>PURPOSE:To enable the test with frequency actually used easily by using the tester for frequency equal to the internal clock, by the constitution of the oscillation circuit, frequency division circuit, test mode signal detection circuit and switching selection circuit. CONSTITUTION:In the Zener diode circuit 6 for test mode detection, the characteristics of Zener diode are selected so that the logic level at point A to the switching selection circuit 7 is 1 only when the voltage more than the used voltage of IC is fed to the IC pin 2. Thus, a normal usage, since the voltage less than the IC used voltage can only be fed to the IC pin 2, the point A is o logic level to the switching selection circuit 7, and the output of the frequency division circuit 5 is selected with the switching selection circuit 7 and given to the internal clock buffer 8. That is, at normal operation, the crystal oscillator circuit 4 is operated with the frequency determined with the crystal connected to the IC pins 1 and 2, the frequency division circuit 5 is activated and internal clock is formed.</p> |
