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Introduction to Real-Time Clock on LCD

Project Requirements

• Interfacing DS1307 RTC Chip and 16x2 Character LCD to STM32 Discovery Board

• Read current time and date information from the DS1307 chip and display it on the LCD

• No Logic Level Shifter will be necessary since the voltage levels between the STM32 Discovery board and the RTC module are compatible. (Check the refernce manuals of the STM32F407xx MCUs and the DS1307 RTC chip.)

Software Layers

• Hardware Abstraction Layer is MCU-Family dependent.

Project Setup

Communication Interfaces

Hardware Setup

• Internal pull-up resistors can also be used instead of external pull-up resistors.

• The RTC module I purchased from Amazon had some design fault. Following product review helped me work around this issue.

  

   

  Poor clone design but works with a simple modifications. The GND pins on both headers are not connected to anything. You will have to run a jumper wire from ground to the side of C2 shown in my picture or pin 1,2,3, or pin 4 of U3. Technically, pins 1-3 of U3 should not even be connected to GND on the PCB. They should be connected to -VBAT along with pin 4 of U2. If you plan on daisy chaining these together remember to run another ground jumper to the header on the other side since it's floating as well. Anyways, the reason I gave these 3 stars is because they were $7 for 5 boards, keep time well, and seem to work of 3.3V or 5V.

  $-$$-$ Collin Miller $-$$-$

Using printf() to Print Messages in STM32CubeIDE Console

• See Using printf() with Serial Wire Viewer (SWV)

Notes

SysTick Timer

• SysTick Timer (23-bit down count timer) will be used to keep the time in this project.

• SysTick Timer frequency is derived from HSI (16 MHz) and scaled by using the prescalar value. (We'll be using 1 for prescalar value which will lead to 16 MHz SysTick Timer frequency.)

  • Down-counting will happen every 1/16000000 seconds (i.e., 62.5 ns = 0.0625 $\mathrm{\mu }$$\micro$s)

  • We want 1 interrupt per second. How many down counts equate to 1 second?

    $\to$$\to$ 16 x 10⁶ down counts!

  • According to the reference manual, down-counting counts to 0 so the actual down-count value to load in the register should be 16 x 10⁶ - 1 (i.e., 15999999).