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SPI Peripheral In STM32F103

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Overview

So, in this blog we will be covering another alternate functionality of GPIO pins i.e SPI (Serial Peripheral Interface). Previously we hve covered following peripherals implementation in STM32F103 MCU’s.

  1. ADC(Analog To Digital Converter) in STM32F103
  2. UART Peripheral in STM32F103
  3. GPIO Peripheral in S32K144 MCU
  4. Clock Peripheral in STM32F103
  5. PWM on STM32F103

SPI is a synchronous and full duplex communication between a master and several slave devices. It is used in devices or sensors in which speed is a priority . It operates at data transmission rate 8 Mbits or more. The protocol uses 3 or usually 4 wires for data transmission and receiver .It is used by various sensors and modules such as OLED Display, BMP280 , RC522 , DAC , Shift Registers etc.

SPI Theory

The SPI uses 2 pins for data transfer SDIN and SDO , SCLK clock for synchronization of data transfer between 2 chips, CE chip select that is used to initiate and terminate the data transfer.

SDI  =  MOSI

SDO  =  MISO

SCLK  =  SCK

CE  =  SS

  • MOSI: MASTER OUT SLAVE IN

    This pin is used to send data from master to slave

  • MISO: MASTER IN SLAVE OUT

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  • SCK: SERIAL CLOCK

    This is used to generate clock to synchronize data transfer between the master and slave device . This is generated by master

  • SS:SLAVE SELECT

    Used to select the particular slave to send data .

Besides SPI communication the SPI interface can switch between I2S communication protocol that is a synchronous serial communication interface. It supports 4 audio standards including the I2S Philips standard, the MSB- and LSB-justified standards, and the PCM standard. The operating modes can be full duplex(4 wires) and half duplex (6 wires)

Multi Mode Configuration

Multiple subnodes can be used with a single SPI main. The subnodes can be connected in regular mode or daisy-chain mode.

 

How Data is Transmitted in SPI

  • Initially SCK is enabled that starts the transmission
  • The master sets the SS line low of the slave
  • Data is usually shifted out with most significant bit  first , shifting a new least significant bit into the same register
  • Data in slave side is shifted into least significant bit of the register
  • Hence after all the shifting is done the master and slave has transferred the data
  • If more data is to be exchanged the registers are reloaded and the process is repeated
  • When no more data transmission is there the master stops toggling the SCK and deselects the slave using SS

 

SPI Peripheral Bus Modes

Before discussing about the various bus modes we will be discussing the clock phase and polarity i.e CPOL:Clock Polarity and CPHA:Clock Phase and it is the combination of CPOL and CPHA that is referred to as Bus Modes.

CPOL = 0 

  • Active state of clock = 1
  • Idle state of clock= 0
  • Means the sampling on the first edge
  •      CPHA = 0 – Data is captured on the rising edge and output on falling edge
  •      CPHA = 1 – Data is captured on the falling edge and output on the rising edge

      

CPOL = 1

  • Active state of clock = 0
  • Idle state of clock = 1
  • Means sampling is on the second edge

 

  •        CPHA = 0 – Data is captured on the falling edge and output on rising edge
  •        CPHA = 1 – Data is captured on the rising edge and output on the falling edge

SPI Features in STM32F103

  • Full-duplex synchronous transfers on three lines  
  • Simplex synchronous transfers on two lines with or without a bidirectional data line
  • 8- or 16-bit transfer frame format selection 
  • Multimaster mode capability  
  • 8 master mode baud rate prescalers (fPCLK/2 max.) 
  • Slave mode frequency (fPCLK/2 max)  
  • Faster communication for both master and slave  
  • NSS management by hardware or software for both master and slave: dynamic change of master/slave operations  
  • Programmable clock polarity and phase
  • Programmable data order with MSB-first or LSB-first shifting 
  • Dedicated transmission and reception flags with interrupt capability  
  • SPI bus busy status flag  
  • Hardware CRC feature for reliable communication: 
     – CRC value can be transmitted as last byte in Tx mode
     – Automatic CRC error checking for last received byte 
  • Master mode fault, overrun and CRC error flags with interrupt capability 
  •  1-byte transmission and reception buffer with DMA capability: Tx and Rx requests

SPI Instances in STM32F103

SPI instances vary from microcontroller to microcontroller from 1 in stmf103c6t6a to 6 in stm32f7 each having different pins NSS pulse mode , TI mode and hardware crc calculations

SPI1 features PA5 as SCK , PA6 as MOSI  and PA7 as MISO

SPI2 features PB3 as SCK, PB4 as MISO and PB5 as MOSI. 

NSS Management in SPI protocol for STM32F103

NSS line can to be driven via 2 modes

  • Software Mode- SS is driven internally by firmware
  • Hardware Mode – A dedicated GPIO pin is used to drive the SS line

Also NSS features NSS output and output disabled mode. Output mode is used only when device operates in master mode and it is disabled allowing mutli master capability

NSS hardware mode must be used in TI mode . CPHA and CPOL are forced to conform to Texas Instrument (TI) protocol requirements. In this NSS signal pulses at the end of every transmitted byte

APPLICATIONS OF SPI PROTOCOL

  • Application 1

    Memory Devices- SD-Card, MMC, EEPROM and FLASH

  • Application 2

    Sensors- Temperature and pressure (BMP280)

  • Application 3

    Control Devices -ADC, DAC, Audio Codec

  • Application 4

    Others- Camera Lens , RTC, LCD , Touch Screen

RFID Module interfacing with STM32F103
W25Q SPI Flash Memory
ST77389 LCD Display with STM32F103
NRF24L01 RF Module with STM32F103

How to Configure SPI Peripheral for STM32F103

We would be using STM32 HAL and STM32CubeIDE for using the SPI peripheral in STM32F103 in this blog tutorial series.

CONFIGURATION IN STM32CUBEIDE

FIG 1- Selecting MOSI, MISO , SS and SCK pins

FIG2 – Selecting the operating mode

FIG3 – Configuring the parameters 

 

  • Intialize the GPIO inittypedef structure and enable the clock to both the port for which the alternating mapping is being used in our case that will be PORT A and also enable clock for the SPI peripheral
  • Using Init API intialize the peripheral 
  • Configure the GPIO parameters such as
  • Pins: This includes the pins that are being used for SPI
  • Mode: This is used to expose the alternate functionality of the peripheral in which condition it is used push , pull or push pull.
  • Alernate : Selects the alternate functionality of the register in our case it will be AF5
  • Pull- Selects if the pin has to be pulled up or not
  • Speed - Determines the speed of operation of the peripheral i.e low, medium, high or even very high in some cases
  • Next we configure the SPI peripheral which in our case will be SPI1 but can be SPI2 in some cases too
  • Mode:The mode of the device has to be set which can be either master or slave
  • Direction:Specifies the bidirectional mode of SPI which can be Direction 2 lines , Direction 2 lines RX only, Direction 1 line only
  • Datasize : The size of data that has to be send which can 8 bits or 16 bits
  • CLKPolarity : This specifies the polarity of the clock which can be low or high
  • CLKPhase : This parameter sets the clock phase which can be 1 edge or 2 edge
  • NSS: This specifies the NSS is managed by software or hardware.The values can be software , hardware input or hardware output
  • Baudrateprescaler : Specifies the amount by which the Baudrate is going to be divided by the values can range from 2 - 256 in the powers of 2
  • FirstBit: This configures how the first bit will be transmission MSB first or LSB
  • TIMode:This sets or unsets the TI Mode i.e if the TI Mode is enable or disabled
  • CRCCalculation: This parameter specifies if the CRC or cyclic redundancy check is enabled or not
  • CRCPolynomial : This is used for polynomial calculations which has to be odd number ranging from 1 to  65535.

SPI Data Handling API Types

SDK Files

  • Stm32f1xx_hal.c
  • Stm32f1xx_hal_spi.c
  • Stm32f1xx_hal_spi.h

The hal.c contains all the macros and function declaration of the GPIO pins the clock configuration and the alternate function mapping of the GPIO pins.The SPI.C function has the declaration and initialization of the SPI function including various parameters , static function and SPI INIT Function . The SPI function contains various macros that establish the various values the functions in SPI.c files functions can attain it includes structure parameters and enumerations.

 

HAL APIs Involved

  • HAL_StatusTypeDef HAL_SPI_Init (SPI_HandleTypeDef * hspi) 
  • void HAL_SPI_MspInit (SPI_HandleTypeDef * hspi)
  • HAL_StatusTypeDef HAL_SPI_Transmit (SPI_HandleTypeDef * hspi, uint8_t * pData, uint16_t Size, uint32_t Timeout) 
  • HAL_StatusTypeDef HAL_SPI_Receive (SPI_HandleTypeDef * hspi, uint8_t * pData, uint16_t Size, uint32_t Timeout)
  • HAL_StatusTypeDef HAL_SPI_TransmitReceive (SPI_HandleTypeDef * hspi, uint8_t * pTxData, uint8_t * pRxData, uint16_t Size, uint32_t Timeout
  • static void MX_SPI1_Init(void)

FUNCTION NAME

HAL_StatusTypeDef HAL_SPI_Init (SPI_HandleTypeDef * hspi) 

FUNCTION DESCRIPTION

This function initializes the SPI peripheral according to the parameters and intialize the handle typedef

PARAMETERS

hspi: pointer to a SPI_HandleTypeDef structure that contains the configuration information for SPI module.

RETURN VALUES

HAL-STATUS

FOR EXAMPLE

FUNCTION NAME

void HAL_SPI_MspInit (SPI_HandleTypeDef * hspi)

FUNCTION DESCRIPTION

This function initializes the Msp of SPI 

PARAMETERS

hspi: pointer to a SPI_HandleTypeDef structure that contains the configuration information for SPI module.

RETURN VALUES

NONE

FUNCTION NAME

HAL_StatusTypeDef HAL_SPI_Transmit (SPI_HandleTypeDef * hspi, uint8_t * pData, uint16_t Size, uint32_t Timeout)

FUNCTION DESCRIPTION

This function transmits certain amount of data in blocking mode

PARAMETERS

  • hspi: pointer to a SPI_HandleTypeDef structure that contains the configuration information for SPI module.
  •  pData: pointer to data buffer 
  • Size: amount of data to be sent 
  •  Timeout: Timeout duration 

RETURN VALUES

HAL-STATUS

FUNCTION NAME

HAL_StatusTypeDef HAL_SPI_TransmitReceive (SPI_HandleTypeDef * hspi, uint8_t * pData, uint16_t Size, uint32_t Timeout)

FUNCTION DESCRIPTION

This function is used to both transmit as well receive certain amount of data in blocking mode

PARAMETERS

  •  hspi: pointer to a SPI_HandleTypeDef structure that contains the configuration information for SPI module.
  •  pTxData: pointer to transmission data buffer
  •   pRxData: pointer to reception data buffer 
  •  Size: amount of data to be sent and received 
  •  Timeout: Timeout duration

RETURN VALUES

HAL-STATUS

FUNCTION NAME

static void MX_SPI1_Init(void)

FUNCTION DESCRIPTION

This function is used to intialize the SPI1 along with the parameters

PARAMETERS

NONE

RETURN VALUES

NONE

CODE

EXERCISE- Transmit data in TX buffer and receive it in the RX buffer

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