设\(S_{n}\)为数列\(\{a_{n}\}\)的前\(n\)项和，且对任意\(n∈N^{*}\)时，点\((a_{n},S_{n})\)都在函数\(f(x)=- \dfrac {1}{2}x+ \dfrac {1}{2}\)的图象上．
\((\)Ⅰ\()\)求数列\(\{a_{n}\}\)的通项公式；
\((\)Ⅱ\()\)设\(b_{n}= \dfrac {3}{2}\log _{3}(1-2S_{n})+10\)，求数列\(\{b_{n}\}\)的前\(n\)项和\(T_{n}\)的最大值．