  We studied numerically the generation of the coherent frequency combs at
second harmonic generation in $\chi^{(2)}$ microresonators via conventional
frequency scan method. It was demonstrated for the first time that under
particular conditions it is possible to generate two-color flat-top solitonic
pulses, platicons, using pump amplitude modulation or controllable mode
interaction approach, if the signs of the group velocity coefficients at pump
frequency and its second harmonic are opposite but absolute values of these
coefficients are rather close. It was revealed that platicons may be observed
on both sides of the linear microresonator resonance (at positive, as well as
negative pump frequency detunings). For the efficient platicon excitation, one
needs simultaneous accurate matching of both microresonator free spectral
ranges and resonant eigenfrequencies. Platicon generation processes were
simulated numerically, excitation conditions and platicon generation domains
were found for different generation methods, and the properties of generated
platicons were studied for the different combinations of the medium parameters.
