Re: A89: Turning LCD Off (and a lot more)


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Re: A89: Turning LCD Off (and a lot more)




I read some more in Johan Borgs nice text 89hw.txt (to be found at my website
http://alh.dhs.org/ti89/)
this passage is particulary interesting: 
----8<--------
The TI-89 contains 2 oscilators, one running at ~10MHz,
turned off when $600005 is written to and restarted by an interrupt not 
"masked" by the bits written. This oscillator controlls the program
execution in the processor.

It can be made run at well over 20MHz, but the calc will not work very
vell, if at all, at above ~16MHz, probably because of a unnecessarily short 
active-time of the 2 bank-select signals for the RAM-banks. This could possibly 
be fixed with some logic. Increcing the frequency from 10 to 16MHz 
doesnt increse the powerconsumption when standby (this oscillator is turned of 
most of the time in this mode) and increses the powerconsumption 
quite linearily for nonstandby-mode. 

The other, runs at ~740kHz when 600015:0 is set, controlling the
timer-interrupts 
and the LCD (and a voltage multiplier used to generate the 16v needed by the
LCD)
"OSC" in this text refers to this oscillator

If both oscillators is turned off, the calc uses almost no power at all, and
this
is probbably what the calc does when the calc is turned "OFF".
------8<-----
(start of my comments here)

So..  if you turn off the second oscillator, you should reduce the power drain
quite much. Unfortunatly you can't then use the timer interrupts, but you can
probably do quite fine without them. just use your own input routines and such.
hmm. Isn't the linkport also generating an interrupt?
Then you could probably do like this; you turn off oscillator 2,  and also
oscillator 1, putting the calc in standby, waiting for link port activity, and
if such comes, it starts up and you can serve that call.
The reason to not just use that standard function for turning off the calc is
that if you do it yourself, you can controll when to light the lcd or not. this
way you take as little power as possible. I guess you don't need the lcd most of
the time you serve thoose link port calls.

hope this tip helps some..
//Olle

Scott Dial wrote:
> 
> I meant to respond to Olle's message before, but am just now getting
> around to it. btw, since it has been more than a week (and I usually
> purge my mail list that often) I decided to give a new thread. I am
> looking to reduce as much power drain as possible, and the I/O bit Olle
> metioned only whites the screen without actually turning the LCD off.
> Any suggestions on how to reduce power drain would be nice... I need to
> still be able to use the link port, so I can't just turn everything off.
> 
> --
> Scott "_Wrath_" Dial
> wrath@calc.org
> ICQ#3608935
> Member of TCPA - tcpa.calc.org


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