Using the STM8S-DISCOVERY GPIOs and interrupt controller to
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1. fe AN3266 YI Application note Using the STM8S DISCOVERY GPIOs and interrupt controller to drive LEDs Application overview This application is based on the STM8S DISCOVERY It demonstrates how to use the STM8S GPIOs and interrupt controller to drive a set of LEDs Once the STM8S105C6T6 is powered up through an USB cable connected to the host PC LEDS LD2 and LD5 start blinking meaning that the programming operation has completed successfully Each time the pushbutton is pressed the interrupt controller asserts an interrupt that is used to control the I Os and change the LED behavior Reference documents m STM8S DISCOVERY evaluation board user manual UM0817 m Developing and debugging your STM8S DISCOVERY application code user manual UM0834 November 2010 Doc ID 17876 Rev 1 1 11 www st com Contents AN3266 Contents 1 Application description 5 1 1 Hardware requirements 5 1 2 Application schematics 5 1 3 Application principle 6 2 Software description 7 2 1 STM8S peripheral configuration 7 2 1 1 GPIOS ries PU RR RE ERR deale ORG ROG AA 7 2 1 2 EXT it aar tg tm anemia den phe yheabia waked TT 7 2 2 Standard STM8S standard firmware library configuration 7 2 3 App2. 76 Rev 1 AN3266 Please Read Carefully Information in this document is provided solely in connection with ST products STMicroelectronics NV and its subsidiaries ST reserve the right to make changes corrections modifications or improvements to this document and the products and services described herein at any time without notice All ST products are sold pursuant to ST s terms and conditions of sale Purchasers are solely responsible for the choice selection and use of the ST products and services described herein and ST assumes no liability whatsoever relating to the choice selection or use of the ST products and services described herein No license express or implied by estoppel or otherwise to any intellectual property rights is granted under this document If any part of this document refers to any third party products or services it shall not be deemed a license grant by ST for the use of such third party products or services or any intellectual property contained therein or considered as a warranty covering the use in any manner whatsoever of such third party products or services or any intellectual property contained therein UNLESS OTHERWISE SET FORTH IN ST S TERMS AND CONDITIONS OF SALE ST DISCLAIMS ANY EXPRESS OR IMPLIED WARRANTY WITH RESPECT TO THE USE AND OR SALE OF ST PRODUCTS INCLUDING WITHOUT LIMITATION IMPLIED WARRANTIES OF MERCHANTABILITY FITNESS FOR A PARTICULAR PURPOSE AND THEIR EQUIVALENTS UNDER TH
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4. en Switzerland United Kingdom United States of America www st com YI Doc ID 17876 Rev 1 11 1
5. flowchart of the application software main loop Doc ID 17876 Rev 1 7 11 Software description AN3266 Figure 2 Main loop flowchart GPIO Configuration EXTI Configuration enablelnterrupts Configures PB1 PB2 PB3 PB4 as output push pull low to drives LD2 4 LD3 LD4 and LD5 Configures PBO as floating input with interrupts to handle the pushbutton Configures the external interrupt sensitivity to falling edge only on PBO This function call enables all the STM8S interruptions ButtonState 0 The selected LED pair starts blinking until the button is pressed again Select LEDs LD2 LD5 Switch LEDs ON Select LEDs LD3 LD4 Switch LEDs OFF ai18463 a 8 11 Doc ID 17876 Rev 1 AN3266 Software description 2 3 2 Interrupt function flowchart Each time an interrupt is asserted the EXTI PORTB IRQhanaler function complements the ButtonState flag and the main loop behaves accordingly see Table 2 Figure 3 shows the flowchart of the EXTI PORTB IRQhandler interrupt function Figure 3 EXTI PORTB IRQhandler function flowchart GPIO Port B interrupt ButtonState flag complemented Back to main ai18464 Doc ID 17876 Rev 1 9 11 Revision history AN3266 3 10 11 Revision history Table 3 Document revision history Date Revision Changes 12 Nov 2010 1 Initial release Doc ID 178
6. interface the microcontroller with external hardware components The GPIO_Init function configures PBO as floating input with interrupt to detect pushbutton events and PB1 PB2 PB3 PB4 as output push pull to control the LEDs EXTI The external interrupt controller is configured through the EXTI SetExtIntSensitivity function to handle the external interrupts on PBO The external interrupt sensitivity is configured to trigger an interrupt each time a falling edge and only a falling edge is detected on PBO Standard STM8S standard firmware library configuration The stm8s conf h file of the STM8S standard firmware library is used to configure the library by enabling the peripheral functions used by the application The following define statements must be present define GPIO 1 enables the GPIOs define EXTI 1 enables the EXTI Application software flowchart Main loop flowchart The code main loop implements the algorithm that controls the LEDs according to pushbutton events The blinking LED pair is selected by setting the ButtonState flag Each time the pushbutton is pressed an interrupt is triggered and ButtonState is complemented see Section 2 3 2 Interrupt function flowchart The main loop code tests ButtonState and selects the blinking LED pair according to its value see Table 2 The Delay function generates a delay between the LED ON and OFF states so that we can see them blink Figure 2 shows the
7. lication software flowchart 7 2 3 1 Main loop flowchart IIIA AUAWA aaa 7 2 3 2 Interrupt function flowchart 9 3 REVISION history 10 2 11 Doc ID 17876 Rev 1 ky AN3266 List of tables List of tables Table 1 List of external components oee 5 Table 2 LEDs configurallon ense e ae ie eee Ge Ree c RR ES Ade dose Dea 6 Table 3 Document revision history WWW KUKIWA Aa 10 ki Doc ID 17876 Rev 1 3 11 List of figures AN3266 List of figures Figure 1 Application schematics RII IAM 6 Figure 2 Main loop flowchart eee 8 Figure 3 EXTI PORTB IRQhanaler function flowchart 9 4 11 Doc ID 17876 Rev 1 ky AN3266 Application description 1 1 1 2 Application description Hardware requirements No on board resources are required Table 1 gives the list of external components required by the application Table 1 List of external components External components Value Comments LD2 LD3 LD4 LD5 Standards LEDs R2 R3 R4 R5 5100 Protective resistors R1 4 7 KQ Pull up resistor R 100 Q Debounce filter C 100 nF Pushbutton Standard pushbutton Application schematics Figure 1 shows how to interface the LEDs and the pushbutton with the STM8S DISCOVERY For details on STM8S DISCOVERY implementation refer to the b
8. oard schematics provided in the STM8S DISCOVERY user manual UM0817 Protective resistors R2 R3 R4 and R5 are mandatory to limit the current to a value that does not harm the LEDs The pushbutton requires a debounce filter RC and a pull up resistor R1 to avoid triggering several interrupts due to the mechanical bouncing of the button Doc ID 17876 Rev 1 5 11 Application description AN3266 1 3 6 11 Figure 1 Application schematics i Pushbutton ai18462 Application principle At startup LD2 and LD5 start blinking meaning that the STM8S105C6T6 Flash memory has been successfully programmed Pressing the pushbutton generates an interrupt which is handled by the application software to drive the LEDs Only one of the two pairs of LEDs LD2 LD5 and LD3 LD4 blink at a time A button event triggers the blinking of the other pair while switching off the first one The LEDs blinking conditions are described in Table 2 Table 2 LEDs configuration Application LED state At startup LD2 and LD5 blink On button event The blinking LED pairs are swapped Doc ID 17876 Rev 1 ky AN3266 Software description 2 2 1 2 2 2 3 2 3 1 Software description The application software uses STM8S standard firmware library to control the general purpose features described in Section 2 1 STM8S peripheral configuration GPIOs The application drives the MCU I Os to
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