title: Modbus RTU with stm32f103 with usart
body: <p><a href="https://i.stack.imgur.com/3hXQs.png" rel="nofollow noreferrer">enter image description here</a>I want to connect my stm32f to pc with modbus.
  I used u USB to rs485 in pc side and sp3485 in micro side.
  The usart1 is configured to work with DMA to transmit and receive data.
  This is a logic analizer picture of my bus, the red is transmitted from pc and blue is micro's answer, the pc to micro is ok. the answer's firs byte (19) is correct. The other bytes first number isn't what I have programmed in transmit register(8 7 7 c b 8 f).
  Also this numbers doesn't change randomly, they are repeating in this answer.
  Where is the problem do you think??
  Tell me if you need more information</p>