I'm designing some circuit using STM32L152RBT6 microcontroller. I'm using STM32L-DISCOVERY scheme as a reference of good STM32 practices. I've noticed that free pins of programmer's MCU aren't connected to ground (of course, they can't be connected at demo MCU in the second part of the circuit). I know that leaving free pins not grounded is acceptable in TTL-based circuits, but CMOS technology (on which STM32 MCUs are based) is different. It uses polar transistors. Ideal polar transistor consumes power only at the moment of switching. Also they're driven by voltage and leaving pins free should increase power consumption because of noise voltages. I've heard that grounding unused pins is a best practice to reduce CMOS power consumption. Should I ground all unused pins like on the scheme?
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