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Thread: Two topics - State Machines & Reliability
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face BY : Richard Prosser email (remove spam text)



This now has triggered a long-time query re these devices.
As I understand it the basis of the state machine is a register containing
data relating to the "state" of the device or process. This is updated by
inputs and used to define the outputs.

Now, the question is how often do I need to refresh it?

In the ideal situation I would monitor the inputs and only change the state
register when required but in the real world there is always the possibility
of data corruption whether from cosmic rays, static discharge etc.

So, the question is, how reliable is the ram in a PIC (or Atemel, Scenix,
etc. etc.)?
Once I've recognised an input condition and acted on it - do I need to
continually refresh the internal registers or can I leave them alone until
something changes. I've always been a bit on the conservative side -
checking & updating as often as convienent but at times this does limit
other options.

If the registers should be refreshed at regular intervals - then what about
the program - surely it is also susceptable to the same sort of thing -
although possibly to a lesser degree. If the data is totally secure once
written, then this is brilliant but somehow I don't really believe it!

Does anyone have any figures and experiences as to this question? I realise
that the  operating environment will be a major factor but even in a benign
environment there may be some corruption mechanisms.

Thanks,
Richard P

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Subject (change) Two topics - State Machines & Reliability

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