[Nucleo] string to signal returns 0

I have a question about module[string to signel]

simulation: If I input a string "0702,0.21M", indeed I can get the desired value " 702" and "0.21".

nucleo monitor and tune: I had sent "0702,0.21M"(by hex:30 37 30 32 2C 30 2E 32 31 4D) by serial port, but I only can get the int or uint type number.

Actually, I guess that there are something else to make the string to float type or double type.

I don't know why, who can help me out?