Abstract: A microcomputer includes a ROM storing various instruction codes including an invalidation instruction code for invalidating a content of an instruction decoder. The invalidation instruction code is read from the ROM and decoded in order to produce an invalidation control signal when a predetermined security execution condition is established. Thus, the security of data contained in the instruction decoder is improved by the ability to physically invalidate an operation of the instruction decoder by writing a predetermined value into the instruction decoder or by erasing its content.

Abstract: A signal level display unit which makes adjustment for correcting of deviation unnecessary and enables cost reduction. An input analog audio signal 26 is divided into seven signals having different frequency bands, converted into digital signal by an A/D converter 22, input to a display controller 25, and temporarily stored in a storage unit 32. A preset recovery time which is input to the display controller 25 through an A/D converter 28 is also stored in the storage unit 32. The value of each signal newly input from the A/D converter 22 is compared with the current value stored in the storage unit 32. When the value of a newly input signal is higher than the current value, the value displayed by a liquid crystal indicator 23 is immediately renewed. On the other hand, when no signal having a higher value than the current value is input, the displayed value is renewed after the preset recovery time stored in the storage init 32 has elapsed.

Abstract: A display control device for a level meter, including a BPF for performing a band-pass filtering of an audio signal to obtain a plurality of frequency components. The BPF obtains an average level of each frequency component of the audio signal. A variable resistor divides a power source voltage. An A/D converter converts the frequency components of the audio signal, the average level and the divided voltage into digital signals. A display controller displays the levels of the frequency components and the average levels thereof on an LCD. The display controller holds a peak value of one of the frequency components or the average levels thereof, and the peak hold time is determined on the basis of the divided voltage. The peak hold time can be freely changed depending on tastes and uses of users.