I want to write a using communication protocol commands to control the axial movement of the program, the process is so of,

Computer sends a string of data to the next bit machine, the machine immediately send a response packet to a computer, shaft began to exercise at the same time,

. After a period of time, when the shaft at the end of the movement process, the machine back a packet b to computers, computer by identifying whether to accept to judge whether the axial movement ended, the packet b

My card in a packet b here, reading the packet b this time how to grasp? Always read? But it stuck program will fail,

What is heard to open a thread, detailed process, please, take a look at