PURPOSE: To obtain output frequencies at any equal intervals by D/A-converting and applying a value set by a counter.

CONSTITUTION: The output of VCO1 is counted by decimal counters 2∼6. Counter 2 shows frequency of several kHz, and counter 3 of tens kHz. The count value of the counter of tens kHz is D/A-converted into analog values of ten levels corresponding to control over frequencies of several, tens, twenties...kHz. Counters 2 and 3 are set to two low-order digits of a desired frequency. The output of VCO1 is set by the D/A converter so that two low-order digits will vary repeatedly by steps between ranges of 45kHz and next 45kHz, for example. With output level 5 assigned by counter 3, tow low-order digits can be set to the range of 50kHz without fail. In short, setting two low-order digits to 55kHz provides oscillation of 55kHz at intervals of 100kHz.