原因状语和目的状语的区分怎样正确原因状语和目的状语,尤其是现在分词作改成分时?如Not wanting to frigh

这里的Not wanting to fright him,I...作的状语成分是原状语,因为这里用的是分词结构,意思上可以理解为I...because I don't want to fright
举个例子：
Being sick ,I stayed at home
也就是 I stayed at home because I am sick.
目的状语通常使用不定式
They stood by the roadside to talk about the plan．他们站在路边为的是谈论这个计划.(目的状语 )
如果这句用分词
They stood by the roadside talking about the plan．他们站在路边谈论着这个计划.(伴随状语)