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For a given MCU, all other things being equal, does the memory capacity impact the power consumption ? A 512kB flash memory would consume more than a 128kB ?

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No. Flash requires no power to maintain its data. It only uses power when actively reading or writing.

The amount of flash has mo direct bearing on the power consumption of the chip.

SRAM, however, does require power to maintain the contents, so the amount of SRAM on a chip vastly affects the power consumption of the chip.

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I'd say that the amount of sram used also affects power consumption. May it be that a modern chip can selectively refresh only used sections saving even more power? –  Vladimir Cravero Jul 9 at 9:03
    
And during the memory access the power consumption won't depend on the memory capacity ? –  milko Jul 9 at 9:05
    
@milko Why would it? One memory cell is one memory cell, be it in the middle of 10,000 or 100,000. The other 9,999 or 99,999 aren't referenced. Yes, the bus interface circuitry may be more complex and consume maybe one or two more pA, but nothing noticeable. –  Majenko Jul 9 at 9:15
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Memory reads are done on the block-level, and e.g. Cortex-M0 uses 512 or 1024 byte blocks, so at any time only that amount of cells has energized column/row lines and subsequently the power loss associated with that (leakage, miller charge, etc.). Chips with less memory than a block size will use less energy for reads and writes, but the effect is quite small. Do take into account that the bulk of energy usage goes into active circuitry; passive effects are quite diminutive. –  user36129 Jul 9 at 9:15
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Take a look at the datasheets for the micros you are interested in. For example the Atmel XMEGA datasheets show that there are no differences due to the amount of flash memory, only the amount of SRAM.

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