Re: A83: Time on TI-83
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Re: A83: Time on TI-83
But, if the timer interrupts are disabled, how will he keep accurate
time?
<<<<<<<<<<<<<<<<<<<<<<<<<+>>>>>>>>>>>>>>>>>>>>>>>>>
See ya,
Mastermind
http://www.bigfoot.com/~mastermind5
>
>I have messed around with such an idea, and you can probably do it
>with
>minimal power. Basically, when you press [2nd]+[ON] to turn off the
>calc,
>it does this:
>
>ld a, 1
>out (3), a
>ei
>halt
>ld a, 11
>out (3), a
>
>What that does exactly, is turn off the LCD by writing a 1 to port 3.
>Then
>it enables interrupts and goes into "halt" mode. When the Z80 is in
>"halt"
>it will not execute further until an interrupt happens. As we all
>know, the
>only key on the keypad with an interrupt is the ON key. Upon pressing
>[ON],
>a interrupt occurs, so the Z80 moves to the next instruction which is
>to
>turn back on the LCD (by writing an 11 to port 3)
>
>It seems weird, but when you turn your calc off, the calc isn't really
>off.
>The RAM is kept alive because of the batteries and the Z80 is still
>alive,
>but just in halt. The only thing that really happened is the LCD is
>off.
>This shows how much the LCD sucks battery power because you can
>probably
>have your calculator off for a year and it would still work next time
>you
>turned it on. This means that the Z80 and RAM use very very little
>battery
>power.
>
>I haven't messed with it too much, but I have tried to do other
>things
>besides a halt after turning off the LCD. For instance, I wrote a 1
>to port
>3 and then started drawing on the screen, then i went into halt (so it
>waits
>for the [ON] key). I followed up with a write of 11 to port 3 (to
>turn the
>screen back on) and then BUFCOPY. So basically, the new rendering I
>was
>looking at was created when the calc was off.
>
>One thing I haven't figured out is how come no other interrupts can
>trigger
>the screen. What about the 200 times a second timer interrupt? That
>doesn't skip over the halt, which means it probably isn't even
>running.
>I've tried using GETKEY, WAITKEY, READKEY all when the calc is off and
>it
>just turned it back on. I think I remember even doing direct input
>and it
>still turned on the calc when I wrote to the keypad port (although
>someone
>may want to correct me on that).
>
>Anyways, a good way to implement a clock would be to shut off the LCD,
>then
>just sit in a loop counting. When the user presses [ON], turn the LCD
>back
>on. I don't know how to detect the ON key, but I know it can be
>done.
>
>-Justin Karneges [Infiniti]
>
>>Also, how would you implement *time* on a calcuator? Surally
>>it would need to know what day it was! An internal clock
>>operating inside some low-power mode using the APD counter?
>>
>>Quized,
>>
>>Bill J Ellis
>>
>>----------------
>>Bill James Ellis
>>Heriot-Watt University
>>
>>B.J.Ellis@hw.ac.uk
>>http://www.cee.hw.ac.uk/~ceebje/
>>
>
>
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