A Real Time Clock (RTC) is a timing element dedicated for keeping time. In many applications, especially where precise timed-operations are needed to be performed, a RTC is a very useful tool. Examples of such applications apart from clocks and watches include washing machines, medicine dispensers, data loggers, etc. Basically a RTC is a timer-counter but unlike other timers of a MCU it is much more accurate. Previous to this post, we explored STM32 timers but those were useful for applications like PWM generation, time-bases and other waveform-related tasks. Those were not suitable for precise time-keeping. In most 8-bit MCUs like the regular PICs and AVRs, there are no built-in RTC modules and so we need to use dedicated RTC chips like the popular DS1302 or PCF8563 when we need an on-board precise time-keeping device. Those chips also need some additional circuitry, wiring and circuit board space. At present, however, most modern MCUs come packed with literally every possible hardware a designer may think of. It is only up to a designer to decide which resources to use from a modern-era micro to meet a specific design goal. Gone are the days when MCUs were manufactured for application specific requirements and also gone are the days of implementing and involving multiple assets in a design. Thus cost, time and space are dramatically reduced, resulting smarter, sleeker and smaller affordable devices. Fortunately STM32s are in that list of those modern era microcontrollers. STM32 MCUs come with built-in RTC modules that require no additional hardware support. This tutorial covers basic features of STM32’s internal RTC and how to use it for time-keeping applications.
Tag Archives: STMicroelectronics
After having played with Analogue-to-Digital Converter (ADC) of STM32 micros, the obvious next internal hardware block to deal with is the Digital-to-Analogue Converter (DAC). As the name suggests this block has just the complementary function of ADC. It converts digital binary values to analogue voltage outputs. The DAC block has several uses including audio generation, waveform generation, etc. Typically in most 8-bit micros, this block is unavailable and its need is somewhat loosely met with Pulse Width Modulation (PWM) block. This is partly because of their relatively less hardware resources and operating speeds. All STM32 micros also have PWM blocks but large capacity STM32s have DAC blocks too. The STM32 DAC block is not very complex and has similarity with the ADC block in terms of operating principle. The simplified block diagram below shows the major components of the STM32 DAC block.
STM32F4xx series micros are far more advanced than anything else similar in the market. Apart from being fast 32-bit MCUs, STM32F4s have rich hardware peripheral support with DSP engine bonus. In terms of capabilities versus price tag, STM32F4s are all-square-winners. In recent times there’s a surge in the STM32 user community. STM32 Discovery boards are proliferating like never before. In several occasions recently, I received tangible amounts of queries from readers regarding integration of STM32F4xx Standard Peripheral Library (SPL) with MikroC Pro for ARM and so even though it is not one of my mainstream posts on STM32 ARMs, I felt that I should address this topic. Previously I showed how to port STM32F1xx SPL for STM32F1xx series devices with MikroC. This post will not be different from the former one – only minute changes. I suggest readers to read the earlier post first before reading this one.
Everything related to digital electronics is related to time. Timer, counter, frequency, pulse width, clock and time are the most common words one may find in this arena. Microcontrollers just like humans need heart-beats and these come from clock sources. Apart from system clock, timers are clock sources that can be used as heart-beats for various applications. All modern micros are embedded with timer-counter modules and generally they are used for generating time bases, counting pulses, measuring time periods of waveforms, generating pulse width modulation (PWM) signals, triggering external devices and timing special events. STM32 micros have several timers designed for such applications. However unlike most 8-bit micros which possess two/three timers with limited functionalities, the timers of STM32s are very elaborate and complex. This explains why documentations related to timer modules take about 25% of any STM32 reference manual.
Before we begin exploring STM32 timers, I must point out that I won’t be able to cover every aspect of all timer modules as they are vast and need lot of explanations, something which is beyond the scope of a single post. This is why in this issue we shall explore the very basics of timer modules enough to get STM32 timers to work.
I remember that once in the beginning I said that I don’t want to buy a programmer/debugger hardware for learning a new MCU like the STM32 and also STM32s already come with built-in bootloader to facilitate programming via USART just like Arduino. Still the second is true. Well what about the first? To my own surprise I actually acquired a number of STM32-related stuffs since the time I started playing and exploring them. I actually bought both ST-Link 1 and 2 programmer-debuggers and several STM32 boards from Waveshare Electronics (http://www.wvshare.com). I believe learning new stuffs is more valuable than anything else.
ST-Link 1 (AKA ST-Link) and ST-Link v2 are both basically the same programmer/debugger hardware with some minor exceptions. ST-Link 2 has 5V tolerance for JTAG interface, it has a bicolour status LED and it also has a separate programming interface for STM8 micros unlike ST-Link 1. There is also an ISOL version of ST-Link2 that galvanically isolates it from its target using optoelectronics.