In this short series of Reducing Noise Issues in Microcontroller Systems blogs, we have looked at noise and how it can disturb the operation of microcontroller-based systems. We have presented some of the “rules” we can use to minimize the impact of noise in our systems.
We have added this blog to our series due to its popularity. It will look at the features of RA microcontrollers, which can make a system more robust in the presence of noise.
The best way to prevent noise problems in any system is to incorporate noise reduction into the design. Understanding the environment in which your system will be operating and what noise sources are present will help you minimize these.
Consider these issues when designing your product. It is much easier to incorporate noise mitigation measures at the beginning of the process than it is to do so at the end.
Renesas RA Microcontrollers have several features to help make your application more robust.
The pins of any microcontroller are vital to its operation. These include supply pins such as Vss, Vcc, and Vcl. Clock pins are also used, as is the reset pin. Analog reference pins and debug pins can be found on the nails. The mode pin controls the device’s operating mode, for example, its boot mechanism.
Noise on these pins can be deadly for your application.
The previous Reducing Noisy Issues in Microcontroller Systems Blog has discussed the importance of a good PCB design in reducing noise. Also, the power supply and grounding systems must be carefully designed, as MCUs today can operate at much higher speeds than older devices. Consider the circuit layout and ground return paths when designing high-speed signals.
When I hear about noise problems in a design, one of the first questions I ask is, do you have to run your device at maximum speed? Sometimes you do, but only occasionally. Top speed is determined by the UART baud rate or the time required to perform a Fast Fourier Transform filter. However, we do not need to run the device at its maximum speed for most designs.
The faster you go, the more likely you are to have problems. You will generate less noise if you run slower. This is because you are using less power and switching less current in your power supply. This can also make your power supply cheaper. Slower is often better for some things.
The RA microcontrollers can be “throttled” to reduce or increase their speed. You can also change the clock dividers on the fly to achieve this. It can add complexity to your application if you need to manage peripheral clocks. However, it is worth looking into reducing the clock speed.
Don’t use the same power supply every time. Also, make sure that it can supply the maximum current. If your power supply drops occasionally, you may have noise problems and other system issues.
Renesas has a useful application note on their website which details injection current that our devices can withstand in order to avoid damage to the RAMCU.
Most of the digital I/O inputs (except for those that support I 2C, devices with Schmitt Trigger input, and devices that do not support these functions) on RA microcontrollers are Schmitt Trigger inputs. This can be used to ensure fast changes in signal levels do not affect the logic of the device. In order to minimize the effects of noise, it is important to take into account the amount of current flowing in and out of each pin. If the system has a lot of noise, current-limiting resistors may be needed on the I/O pins.
These filters are also found in peripheral input pins, such as UART interfaces, SPI interfaces, I 2C, as well as timer inputs. It is crucial to choose the correct filer clock to get maximum performance from these filters. This can often require some trial and error.
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Communication interfaces pose a significant problem in a typical microcontroller’s design. They are naturally connected to the external world and often introduce high-speed signals. It is essential to take care of and use external protection circuitry depending on the external environment.
In a previous blog, we discussed the importance of a sound clock system in ” Creating reliable crystal oscillator circuits for your MCU design.” Ensuring the external crystals are matched correctly to the PCB design and the device is imperative. It is essential to do this using a 32kHz low-speed oscillator. These are notoriously susceptible to issues in noisy environments. Checking your oscillator provider for the correct circuit to work with our devices is always a good idea. It is less likely that a stable oscillator with lots of margins will cause problems.
Watchdog timers can be a great way to recover your application if noise is the cause of a crash. However, you must know how to use them correctly.
The watchdog timers on RA microcontrollers are available in two varieties. One is the standard timer, which can be clocked by various clock sources that come with the microcontroller. This watchdog timer is used to test the code execution of an application and detect any malfunctions or unexpected operations. It is usually switched off when low-power applications are running. When it runs out of time, this watchdog can trigger a RESET.