title: STM32: UART DMA does not start correctly
body: <p>I am using two STM32H743 connected via RS232. These two modules connected to same power.
  They use UART with DMA. When I turn on modules at the same time, UART and DMA starts correctly.
  But when i restart one of the modules while other is awake, the reset module's UART and DMA does not start therefore they cannot communicate with each other.<br>
  This problem is also happened before with STM32F4 series. MCU is connected to FPGA and they communicate via UART. When FPGA starts before MCU, DMA and UART does not start properly. What could cause this problem?
  Do i need to have a high-z or floating pin states before starting UART?</p>