If we are talking of B.Tech or B.E well the university where you will study will have a fixed syllabus and the specialization will be Mechatronics. Now the first year is mostly common for all engineering students across all branches but the second year on the subjects taught are mostly pertaining to the specialization. Here I must tell you that the syllabus will differ from institute to institute. You can do mechanical engineering and then specialize in mechatronics in your post graduation also. check the university in which you are interested and look up their B.Tech mechatronics syllabus to get a better idea. I must also tell you that not all universities may offer mechatronics. for eg manipal university syllabus is given at https://manipal.edu/content/dam/manipal/mu/mit/documents/CO_MECHATRONICS--2014.pdf