Re : A92: Re: Link cable
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Re : A92: Re: Link cable
well: the signal send is a square signal...
Here is am email send to me by mel tsaiv ( he made a mem expander ) to
explain this: it was long ago.... Do not forget that we can now control how
are the wires: there is some info on this on :
http://www.flash.net/~bryanr/extend/
at least , there was a file to explain the control of wires... but i can' t
find it anymore in my disk...
<<Let's say Calc1 brings the red wire low (i.e. zero volts), then calc2
brings the white wire low in acknowledgement. This transaction
signals that Calc1 is sending a "1" bit to the other calculator, and
this is how the TI link protocol works (asynchronous transmissions).
But, what happens when Calc1 sends a "0" bit? It brings the white
wire low this time, and then Calc2 brings the red wire low in
acknowledgement. This "dual use" of the two link wires makes it
extremely difficult to record, for a number of reasons. First, you'd
need to add some diode logic (not a trivial task) so that you won't be
recording the actions of Calc1, because if you did this would screw
the transmission up (assuming you have two calculators transmitting
something, and you're attempting to record this transaction).
Second, the speeds of calc1 and calc2 can vary widely depending on
each other's battery levels, and the chances are slim that you'll be
exactly aligned when you play it back, and this will result in a
screwed up transfer! A couple milliseconds off, and the whole
transmission goes bad. This is a highly unstable and innacurate
thing, because the chances for misalignment are very great! Regular
cassette tapes and recorders aren't designed for such accuracy.
So, to solve this then you'd probably need to add some sort of
synchronization circuitry intervening between the two calculators, so
that they are timed to an exact frequency. This would involve perhaps
some sample and hold circuitry, or maybe some digital logic
synchronized to an oscillator. All this adds up to one huge mess, and
it's probably easier to just use a microprocessor.
Even if it did manage to work, you'll be LUCKY to get more than 80-150
kilobytes on an entire 90 minute tape, and that's IF you want to wait
90 minutes to transfer that amount!!! Then you're stuck with the more
traditional tape backup problems, such as finding where certain items
are stored without having to play the whole tape back, etc.
There are actually a couple more major headaches involved with using a
cassette recorder, but I don't have time to go into them. So, my
final advice: forget about cassette tape backups :).
-Mel
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
-The TI-Memory Expansion Homepage
-http://www.egr.msu.edu/~tsaimelv/expander.htm
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>From tsaimelv@PILOT.MSU.EDU>>
Mathieu, <hm lacage@aol.com>