Have been working on "Rupee", and was curious that some scripts have specific Unicode points for their rupee symbol whilst others don’t. That led me to pre-Unicode Indic encoding schemes.
We have articles for ISCII and TSCII, but I haven’t found anything for TAM and TAB.
Anandakrishnan, M. (2010-06-24). "Tamil computing: the present and the future". The Hindu. Promoting TIC-2010 conference, but also covers background of 1997 and 1999 conferences, formation of INFITT, mentions TAM and TAB, …
Kalyanasunderam, K. (2007). "Introduction to Tamil Information Technology"(PDF). INFITT. Retrieved 25 October 2019.. Wide ranging slide deck. Mentions multiple encoding schemes. Has code tables for TAM and TAB, but they are hard to read.