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Nothing left to be invented in embedded control (Part 2)

Posted: 25 May 2015 ?? ?Print Version ?Bookmark and Share

Keywords:microcontroller? MCU? Flash? PWM? CMOS?

"There is nothing new to be discovered in physics. All that is left is more and more refined measurements."Lord Kelvin, address to the British Association for the Advancement of Science C 1900 (disputed)

I am obviously paraphrasing this famous (although disputed) quote from Lord Kelvin, who was addressing the British Association for the Advancement of Science in the year 1900. One hundred and fourteen years later, it might seem like this quote could be applied to the world of embedded control. But this would be just sad, and, thankfully, it is far from the truth. There is plenty of innovation happening in embedded control, and it is occurring right now, in front of our eyesin the 8bit world!

In the first part of this short article series, we saw how 8bit microcontroller cores are so small that relatively large CMOS process geometries can be used effectively to operate at higher voltages, drive higher current loads (up to 100 mA on selected MCUs) and to provide large margins of noise immunity, hence robustness. But, when it comes to processing speed, there is a clear disadvantage that they need to neutralise. The way they can do that is by changing the fundamental rules of the game, creating an arsenal of what we called the Core Independent Peripherals.

Core independent peripherals
The basic idea behind these new peripherals is that, once set up properly, they will operate independently and relieve the microcontroller core from the heavy lifting of the task at hand. This allows the use of a smaller MCU, operating at a lower clock speed, and idling (or even entering standby mode) for maximum cost, power and complexity reductions.

In the first part of this article series, we looked at the first two examples of core independent peripherals: the Signal Measurement Timer (SMT) and the Configurable Logic Cell (CLC).

The SMT proved to be useful in our example, helping to achieve a significant savings in power consumption via a reduction of the software complexity and required clock speed by as much as two orders of magnitude.

The CLC, by itself, was shown in the first example as an important tool for the reduction of power consumption in battery-operated applications by performing combinatorial and sequential input filtering. This produced a "smart" wakeup for an MCU that was otherwise spending most to all of its time in a standby (eXtreme Low Power) mode.

Reaching deep
It would be very wrong if I gave you the impression that the CLC is just a tool for smart input filtering. Each CLC block has access to a large number of signals (16 to 32 in current models) that reach deep inside the microcontroller and its peripherals. These go far beyond the usual I/O structures connected to the device pins. They include most/all of the outputs from the timers, PWMs, and basic modules, as well as all the "other" core independent peripherals. In their turn, the outputs of each configurable logic block can be published on external pins or can be re-routed internally directly as an input (or trigger) of any of the peripherals available on chip.

Now things get really interesting because it is at this point that we can start building "new" peripherals by combining core-independent and traditional peripheral modules to perform new functions. These functions can be very specific and unique to the application and market segment, using what is otherwise an inexpensive family of general-purpose microcontrollers. Even more interestingly, because each CLC (connecting) block is configured at run-time via special function registers (RAM), the function of the new peripheral modules can change while the application runs.

Creating custom peripherals
As we did in Part 1, we will now review a practical example application where the core independent peripherals' ability to be configured and combined together can be best appreciated.

Our example application will be a "smart" power supply of sorts. A low-cost, general-purpose microcontroller will provide the intelligence. While we won't detail the control algorithm or topology of choice, this example will suffice for the purposes of our conversation, to specify that an output in the form of a PWM signal will have to be generated. Further, we will specify that the desired output frequency (Fout) be at least 500kHz, to reduce component size and cost, and the output resolution will be optimised for maximum stability in a 10% range around a set point centred at a 50% duty cycle.

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