等待RS字符串返回，或是时间到达 Comm是通信控件名称 RS是欲等待的字符 DT是最长的等待时间 正常时返回值是所得的完整字符串，不正常时返回值是空字符串-' Waiting for RS strings to return, or the time to reach the' Comm is a communication control name ' RS is the character you want to wait' DT is