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Flash speed

Atiom
Intellectual 565 points


Hello!

Why is it not needed to insert wait states for the FLASH memory to operate properly, as we increase the MCLK frequency, in the same fashion that it is needed for the FRAM to operate above 8MHz?

I mean, does the FLASH always operate at the same frequency regardless of the CPU speed? If so, at what frequency does it operate?

Thanks!

  • 0
    Guru 12956 points

    I think Flash operates at a speed equal to or higher than the MCU's maximum MCLK speed, so wait states are never required.  FRAM is unfortunately hampered by 8MHz maximum speed.  Hopefully future generations of the FRAM tech will raise that speed a bit.

  • 0 in reply to Eric Brundick
    Guru 227245 points

    Flash cells are very slowly written to, but reading them is as fast as the other part of the system, (rather simple CMOS gate logic=.

    FRAM, however, is erased when being read, so it needs to be written again after each read. Writing is by magnitudes faster than writing flash. But since each read has to be followed by a write, before the next cell can be read, FRAM is limited to 8MHz for reading as well as writing. There is a volatile cache that stores the last FRAM reads, so not every FRAM access requires the waitstates, but its use depends on the code. And it makes estimating execution times difficult if above 8MHz MCLK.

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