Hi Ramachandran. I am happy to answer your doubts. The first question you have asked is whether the HSC/Equivalent registration number is the same as Roll number in the 12th mark sheet. Yes, both are the same. Answering your second question, the code next to each subject is called the subject code. Do not confuse it with the registration number. I will give you examples for better understanding.

Roll No. be like - 4604614, 4136326, and subject code be like 301, 042, etc.

This link directs you to Careers360 registration guide, where you can find step by step procedure to apply for TNEA. Have a look into it. https://engineering.careers360.com/articles/tnea-application-form

If you further have doubts, you can contact DIRECTORATE OF TECHNICAL EDUCATION - DOTE. Their help desk number is 044 2235 1014 . DOTE works on weekdays from 10 am to 5.40 pm and on Saturdays, they work from 10 am to 3.55 pm only. Sundays are holidays.

Hope this was helpful. Thank you. Stay safe.