[A83] Re: NMI
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[A83] Re: NMI
> When the calc turns off, the display is shut off, then
the calc goes into
> low power mode while waiting for an interrupt. The CPU
is never actually
> shut off. The on key generates an interrupt, which
causes a jump to the 38h
> interrupt handler. When the calc is first powered on
from a no power state
> (the only time it is truely powered on), it starts at
00h. It is likely
> that there are some variables that it reads to determine
if it is necessary
> to reset the memory when it is first started. It must do
this, or the
> lithium battery that saves the ram would be useless.
>
I already knew this. That's why I used the quotation marks
around "off"... The question was actually about poweroff
while not in this pseudo-off state, because I don't know
what the TIOS modifies before jumping to the halt loop
(besides turning off the LCD). But it's quite possible that
the code at zero takes care of this situation, too (if
there is really any need to do so).
Just an example of what I was thinking about: if we are at
the home screen, pressing simply On has no effect. Then we
take out the batteries without using first the proper
2nd+On TIOS shutdown mechanism. The TIOS somehow keeps
track of whether the calc is off or on, if I'm right. After
replacing the batteries we can see that it could not
be "tricked" to believe that the calc is still on, because
if it was so, pressing On would have no noticeable effect,
only after pressing 2nd+On.
That's why this question came into my mind seeing "NMI". I
thought that there was an interrupt indicating that power
was on the verge of disappearing.
PG
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