/**
  @page USART_Communication_Tx_IT USART Transmitter example (IT mode)
  
  @verbatim
  ******************** (C) COPYRIGHT 2016 STMicroelectronics *******************
  * @file    Examples_LL/USART/USART_Communication_Tx_IT/readme.txt 
  * @author  MCD Application Team
  * @brief   Description of the USART_Communication_Tx_IT example.
  ******************************************************************************
  * @attention
  *
  * Copyright (c) 2016 STMicroelectronics.
  * All rights reserved.
  *
  * This software is licensed under terms that can be found in the LICENSE file
  * in the root directory of this software component.
  * If no LICENSE file comes with this software, it is provided AS-IS.
  *
  ******************************************************************************
  @endverbatim

@par Example Description

Configuration of GPIO and USART peripheral to send characters 
asynchronously to HyperTerminal (PC) in Interrupt mode. This example is based on the 
STM32F1xx USART LL API. The peripheral initialization 
uses LL unitary service functions for optimization purposes (performance and size).

USART Peripheral is configured in asynchronous mode (115200 bauds, 8 data bit, 1 start bit, 1 stop bit, no parity).
No HW flow control is used.
GPIO associated to User push-button is linked with EXTI. 
Virtual Com port feature of STLINK could be used for UART communication between board and PC.

Example execution:
On press on push button , USART TX Empty interrupt is enabled.
First character of buffer to be transmitted is written into USART Transmit Data Register (DR) in order to initialise transfer procedure.
When character is sent from DR, a TXE interrupt occurs. 
USART IRQ Handler routine is sending next character on USART Tx line. 
IT will be raised until last byte is to be transmitted : Then, Transmit Complete (TC) interrupt is enabled 
instead of TX Empty (TXE). 
On last byte transmission complete, LED2 is turned on.
In case of errors, LED2 is blinking (1sec period).

Program is written so that, any new press on User push-button will lead to new transmission of complete buffer.

@par Directory contents 

  - USART/USART_Communication_Tx_IT/Inc/stm32f1xx_it.h          Interrupt handlers header file
  - USART/USART_Communication_Tx_IT/Inc/main.h                  Header for main.c module
  - USART/USART_Communication_Tx_IT/Inc/stm32_assert.h          Template file to include assert_failed function
  - USART/USART_Communication_Tx_IT/Src/stm32f1xx_it.c          Interrupt handlers
  - USART/USART_Communication_Tx_IT/Src/main.c                  Main program
  - USART/USART_Communication_Tx_IT/Src/system_stm32f1xx.c      STM32F1xx system source file


@par Hardware and Software environment

  - This example runs on STM32F103xB devices.
    
  - This example has been tested with STM32F103RB-Nucleo board and can be
    easily tailored to any other supported device and development board.

  - STM32F103RB-Nucleo Set-up
    In order to select use of Virtual Com port feature of STLINK for connection between STM32F103RB-Nucleo and PC,
    User has to set USE_VCP_CONNECTION define to 1 in main.h file.
    If so, please ensure that USART communication between the target MCU and ST-LINK MCU is properly enabled 
    on HW board in order to support Virtual Com Port (Default HW SB configuration allows use of VCP)

    If VCP is not used (USE_VCP_CONNECTION define set to 0 in main.h file), Connect USART1 TX/RX 
    to respectively RX and TX pins of PC UART (could be done through a USB to UART adapter) :
    - Connect STM32 MCU board USART1 TX pin (GPIO PA.09 connected to pin 21 of CN10 connector)
      to PC COM port RX signal
    - Connect STM32 MCU board USART1 RX pin (GPIO PA.10 connected to pin 33 of CN10 connector)
      to PC COM port TX signal
    - Connect STM32 MCU board GND to PC COM port GND signal
    
  - Launch serial communication SW on PC (as HyperTerminal or TeraTerm) with proper configuration 
    (115200 bauds, 8 bits data, 1 stop bit, no parity, no HW flow control). 
    Port should be selected according to USE_VCP_CONNECTION value.

  - Launch the program. Press on User push button on board to initiate data transfer.

@par How to use it ? 

In order to make the program work, you must do the following :
 - Open your preferred toolchain
 - Rebuild all files and load your image into target memory
 - Run the example


 */
