Hello,
AP EAMCET- Andhra Pradesh Engineering, Agriculture, Medical Common Entrance Test is state leveo entrance exam for admission to above stated undergraduate courses offered by various colleges in Andhra Pradesh.

ECET- Engineering Common Entrance Test is conducted for lateral admission to 2nd year in B.E B.Tech courses offered by the various engineering colleges of the state. It requires diploma or a B.Sc degree to be eligible for admission.

So, while EAMCET is conducted for admission as first year in various courses, ECET is conducted for direct admission to 2nd year of Engineering courses.

Follow this link for more information
https://engineering.careers360.com/exams/ap-ecet
https://www.careers360.com/exams/ap-eamcet

Good luck