Re: Turbo charging 85?


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Re: Turbo charging 85?



According to what I have learned thus far in my Electrical and Computer
Engineering courses, it _must_ take more power to run the TI calculators
or any other processor faster. This is because it takes a fixed amount
of energy to change the state of the logic on the CPU. Each clock cycle
(which requires draining capacitors from 5v (logic 1) to 0v (logic 0) or
charging them from 0 to 5v ) ends up taking a certain amount of energy.
Runing the TI faster means more clock cycles per second, which means
more energy consumed per second, which means more power is dissipated by
the cpu.


Looking at it another way, if the calculators work when they're
overclocked, then at the 6mhz speed set by ti the chip's logic has more
than enough time to change states (it takes a certain amount of time as
well as a certain amount of energy to switch logic states). Once the z80
has finished its instruction, it consumes almost no energy until the
next clock cycle starts. So it may be that an unmodified TI85 CPU's
logic is idle half the time it's on, while the overclocked ti85 spends
more time per second executing instructions and less time waiting for
the next clock pulse. (Note that I said "idle half the time" for
illustrative purposes; I have no idea what the actual percentage is.)


  There is a lot more to be said about power consumption. For example,
different instructions require different amounts of energy, depending on
how complex they are. I would hope the z80 has an instruction like halt
or noop that does nothing. This instruction would require fewer logic
gates to be switched than a "real" instruction that adds things or
whatever. If the Ti has an instruction like this, then I bet most of the
time the calculators are on they are executing these instructions. This
could be between each keystroke when you're at the home screen or
entering a matrix, or any other time you're not sitting there wishing
the thing would go faster, but not when you're graphing or executing a
program, because these run as fast as possible. So depending on whenther
you use your calculator to calculate or to play games, you could see a
small or drastic decrease in battery life due to overclocking, just
becasue you might not notice the effect of an extra million noops per
second as much as an extra million instructions per second while gaming.
Again, this is assuming that the z80 can do power management like this.


  Anyway, I'm not going to overclock my ti85's cpu anytime soon. There
are so many things that can go wrong, from melting something with a
soldering iron to setting the clock a little too fast, which could
produce random errors in doing math and running programs. These errors
might very well occur sometimes and not others just depending on the
temperature of the CPU...


  My friend bought a new pentium last fall with a 512k cache module from
a very respectable mail order company that is huge with a 4 letter name
that rhymes with "fell". Anyway, the cache was just a tad slower than
the memory bus clock. He spent weeks trying to track down software bugs
after he got it. Finally, after he killed win95 and installed NT, and
the bugs were still there, he fingured it might be hardware and started
pulling parts off his motherboard until he found that the pc worked fine
with the cache disabled. He got a new cache module, and the pc works
great now. The moral of this story is that every semiconductor device is
a little bit differen from every other one because of small defects in
their manufacture. Odds are that zilog aims for say 7mhz when it makes
its 6mhz chips so that the ones that are a little too slow are still
fast enough to sell as 6mhz parts to TI. So just becasue some people can
get their calculator to run faster doesn't mean that yours will work
even if you follow the instructions carefully. The other moral of the
story is all of the hassle he went through wasn't worth the speed
increase he got out of getting the fancy 512k cache module when the 256k
modules were more reliable last fall when the main manufaturer of 512k's
didn't have it's act together. The situation wasn't really my friend's
fault, because he was using the computer as it was designed, but it will
be your fault if you mess up your calculator while attempting to modify
it.....


Well, that's more than my 2 cents worth, but I hope this at least
answers the question about battery usage


-Jonathan Samuel


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