Re: TI-H: 0.1 capticitor
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Re: TI-H: 0.1 capticitor
On Mon, 9 Dec 1996 21:20:58 +0000, you wrote:
>> >I have been wondering for months where to find a smaller cap, and I
>> >recently realised that something that small may actually overclock the
>> >TI-85. If you wan those speeds, just take out c9 and leave it empty.
>>
>> If one was to do this, then the wave being sent to the Z80 would be
>> totally flat, and would have no pulse in order to regulate it's internal
>> clock. Therefore, the Z80 would freeze, and possibly be ruined.
>
>Actually, this is the most common method of accelerating the calc...
>I don't think it freezes it. :) There is still a _very_ small
>capacitance, simply because the traces are still there, and this
>results in a very high frequency (from what I have heard, about 3 to
>3.5 times faster). And even if the capacitance went to absolute
>zero, the frequency would theoretically become infinite. Wouldn't
>that be neat? :) (Of course, the circuitry wouldn't be able to
>handle it...).
>
It's not the traces that are giving it the capacitance, that would
only be maybe 20-40 pF. Most integrated circuits have their own
"input capacitance" that can be in the hundreds of pF, and this causes
it to oscillate even though the capacitor was removed. This is also
why you can't have more than 5-10 devices connected to the same data
line, because all the capacitances added up will throw the timing off
(depending on the logic family). Remember that the oscillatory rate
also depends on the resistance of the RC network, and if it's a very
small resistance the capacitor will charge quickly and the clock rate
will go up.
-Mel
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