H1 90 degree pulse, then proton cross polarization to enhance the C13 signal. If there is no N15 180 pulse, it would be a C13 spin echo after 180 degree pulse with each rotor cycle. If N15 180 degree pulse applied, it would be C13-N15 dipolar evolution period after each pair of 180 degree pulse.

Ref: Introduction to Rotational-Echo, Double-Resonance NMR by Terry Gullion 1998.