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Getting Started and Peripheral Coding STM32 MCU's STM32F1

GPIO Peripheral in STM32F103 MCU

Table of Contents GPIO Theory So now  we’ll talk about GPIO pins . GPIO stands for general purpose input output pins; they are the means for communication between the microcontroller and the external world (using sensors etc).It is signal that arrives on these pins or a signal that is sent or written on these pins that facilitates this communication. These pins can be configured to act as input or output  via the application software(in our case stm32cube ide). The programmer can configure the pins as LOW or 0V or HIGH or 3.3V(or 5V ). These GPIO pins can also be configured to act as  special purpose pins as well where their alternate functionality is exploited . These alternate functionality includes UART , ADC , SPI etc . In the case of UART communication, Transmitter(Tx) and Receiver(Rx) pins are required. GPIO pins can be configured to act as TX or RX pins . Even in ADC the pins are configured to act as Analog pins having 12 bits of resolution . The alternate functions of various pins are shown below: Input floating Input pull-up Input pull-down Analog Output open-drain Output push-pull Alternate function push-pull Alternate function open-drain GPIO Peripheral in STM32F103 All the pins of STM32F103 are grouped in multiple ports as PORT A, PORT B, PORT C As can be seen from Pin configuration chart in the PA1 stands for Port A Pin 1. There are 37 GPIO pins in stm32f103 which are divided as PORT A with 16 pins, PORT B with 16 pins, PORT C with 3 pins and PORT D with 2 pins. Each GPIO  port  has two 32-bit configuration registers (GPIOx_CRL, GPIOx_CRH), two 32-bit data registers (GPIOx_IDR, GPIOx_ODR), a 32-bit set/reset register (GPIOx_BSRR), a 16-bit reset register (GPIOx_BRR) and a 32-bit locking register (GPIOx_LCKR). In the register names, x stands for the port to which pin belongs. If we are configuring pin PA1, it has Port A then registers would be accessed by GPIOA_CRL and etc. Out of above-mentioned registers, GPIO peripheral has 2 most important registers: Direction Register(GPIOx_CRL, GPIOx_CRH)</h3 > Direction register: Set the corresponding pin as input/output pin. Data register(GPIOx_IDR, GPIOx_ODR)</h3 > Data register: where we set the Logic level (High (1)/Low (0)), for the corresponding pin if it is configured as output pin or we read the Logic level (High (1)/Low (0)), for the corresponding pin if it is configured as input pin. Pin Configuration Chart Pin Definitions GPIO Peripheral Block Diagram in STM32F103 First after selecting the pin the port is decided Then after following the arrow the busses are selected based on it: APB/APB1 or AHB After which the clock is enabled to the particular port using either __HAL_RCC_GPIOX_CLK_ENABLE() function or using the RCC AHB1 peripheral clock enable register and selecting the port to which clock has to be provided by enabling it. Methods to configure the GPIO Peripheral Configuring the busses i.e AHB1, AHB2, APB1, APB2 . The AHB bus is faster than APB bus and in case of certain modules they are connected to the same bus .Hence it depends upon the application which bus to use. As can be seen from the picture below the AHB1 takes clock to PORT A , PORT B , PORT C etc . Hence to initialize a pin to a particular port the in RCC AHB1 clock enable register GPIOEN is set to 1 (For Port A GPIOAEN , For Port B GPIOBEN etc) Enabling the clock to that port otherwise the particular pin will not be functional  Creating an instance of the structure and then using the members of the structure set the following:- PIN – Takes the pin no as input GPIO_PIN_X {where X -0 to 15} MODE– Selects the mode the specified pin is supposed to work in . It takes in value Output Push Pull ,Output Open drain PULL- It selects the initial value of the pin and takes value no pull up no pull down, pull up or pull down SPEED- Selects the speed of the working of the specified pin i.e low, medium or high ALTERNATE- Specifies the alternate function performed by the pin UART TX OR RX , ADC etc, GPIO Peripheral SDK using STM32HAL We are going to use STM32 HAL SDK for using the GPIO peripheral of the STM32F103. STM32HAL is a very versatile and robust Software package for using Peripherals of the STM32 Microcontroller family. To know more about STM32HAL, refer to this link. Each STM32 HAL has drivers for all the peripherals of the STM32 Microcontroller(One can navigate to the Driver folder in the STM32F1 HAL local repo installed). These drivers can be configured and enabled to use in the project via the STM32 CubeMX configuration tool, which is also integrated into STM32CubeIDE( just like told in the above section for configuring GPIO peripherals). Will be digging into that part, in the next section. For now, let’s understand the STM32HAL GPIO SDK for STM32F103 MCU. stm32f1xx_hal_gpio.c: This file consists of various macros and  is responsible for the intialization and configuration of the functions which in turn configures the peripheral. stm32f1xx_hal_gpio.h: consists of various structure definitions that help configure various parameters of the pin, enumeration, and various macros stm32f1xx_ll_gpio.c & stm32f1xx_ll_gpio.h: GPIO Low-level driver source/header file, contains functions that configure the GPIO Peripheral registers at the hardware level. These files are the ones that actually interact with the hardware and make it configurable to our needs.  STM32 HAL Functions for GPIO Peripheral Functions are set of instructions that required to perform certain tasks. In general, a function is first declared in header file(.h) and then it is definied in source file(.c) and then called in main.c or application code. It is of the form function return data type, function name and function arguments. In Embedded functions are required to initialize a peripheral or configure it on the basis of various parameters which are passed on using arguments. This information is then passed on to the registers.  List of functions used

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