We demonstrate the generation of dissipative soliton resonance square pulses from a co-doped Er:Yb double-clad fiber ring laser operating in an all anomalous dispersion regime. The obtained pulses have a repetition rate of 672 kHz and a pulse energy of 409 nJ. By carefully adjusting the polarization controllers while increasing the pump power, the square pulse can split into a series of identical equally spaced smaller square pulses up to the 13th harmonic of the fundamental repetition frequency. The average output energy of the square pulses follows a scaling law versus the harmonic order