  We studied numerically the generation of the two-color flat-top solitonic
pulses, platicons, in the microresonator based doubly resonant optical
parametric oscillator. We revealed that if the signs of the group velocity
dispersion (GVD) coefficients at interacting harmonics are opposite, platicon
excitation is possible via pump amplitude modulation or controllable mode
interaction approach. Upon pump frequency scan generation of platicons was
observed at positive pump frequency detunings for the normal GVD at pump
frequency and at negative detunings in the opposite case. Interestingly, we
found the effect of the transformation of the flat-top platicon profile at
half-frequency into the bell-shaped bright soliton profile upon frequency scan.
For platicon excitation one needs simultaneous accurate matching of the
microresonator free spectral ranges at interacting harmonics and resonant
eigenfrequencies. Excitation conditions and platicon generation domains were
found for the different generation methods, and properties of the generated
platicons were studied for various combinations of the medium parameters.
