Subject:
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Re: Digicomp II
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Newsgroups:
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lugnet.technic
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Date:
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Fri, 14 Dec 2007 19:51:25 GMT
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Viewed:
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11338 times
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In lugnet.technic, Alexander Holroyd wrote:
> > flip-flop gates for a working model of Digi-comp II:
> >
> > http://www.brickshelf.com/cgi-bin/gallery.cgi?i=2859643
>
> I for one can hardly wait to see the video of this.
> And I would love to see more explanation and construction
> details too!
Well, I finally got the video put together, with some narration to explain a
little bit of what's going on. I wish I could put it on YouTube a bit bigger
(it's all 640x480, but YouTube seems to compress it down).
http://www.youtube.com/watch?v=SYi9sJkS19Q
(PS- sorry about the narration, but there was too much to try to explain... & I
have a cold :| ).
As to how it works, there are a couple of automated modes. Generally, if you
want to add two numbers you put one in the accumulator (A), and one in the
Memory register (M), and set the Q register to 1 (OK, "001"). Releasing a stream
of balls into the three blue-coded gates (a distributor) simply adds with carry
each bit of the M register into the accumulator. One of these four balls also
falls into the Q register before doing its add duties, decrementing the Q
register by one for every four balls released. Since each ball triggers the
next, the computer will continue adding M into A until a ball "falls out" of the
machine by underflowing the Q register.
There are a series of "Accumulator mode" switches on the far right edge that
normally direct balls to the bottom, but can be switched to the right to perform
a complement operation on the accumulator. With a flip-flop at the top and
bottom, the machine actually automates a "@'s complement" operation, flipping
the mode switches, dropping a single ball into the accumulator to complement it,
switching the mode switches back to normal, and dropping a final ball into the
top of the accumulator to perform an "add 1" operation.
By using repeated addition and 2's complement, it's very easy to set it up to
add, subtract, and multiple (or even combinations of those). It can also do
division, although it's slightly more confusing and I've not really puzzled it
out in detail yet. It can also be set to just count balls (each ball triggering
the next), and to clear the accumulator (a single ball passing through the 2nd
level resets all the accumulator gates to the right). To keep things straight,
I've not labeled the 0 & 1 sides of each gate, but instead but the decimal
number they represent on one side (so if you see a gate pointed to the number
"16", you know that that bit represents 16 in that position). The initial or
"home" state for all the switches is also noted by 1x1 yellow plates for ease of
reseting.
I can think of a number of improvements, actually - but it took a special
order from S@H (thank goodness for Technic beams in on-line PAB! It uses
something like 80 of them) just to get some of the parts I thought I'd need.
This went through a number of revisions (at one point it stood vertically, but
that took even more LEGO), but I'm reasonably happy with the result.
Rafe, if you can blame me for inspiring your GBC counter, I can blame you now
for a couple of large PAB orders to realize this. Yes, I'm going to try to
incorporate it into a "proper" GBC module at some point, & haul it up to
Brickworld.
--
Brian Davis
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Message has 2 Replies:
 | | Re: Digicomp II
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| "Brian Davis" <brdavis@iusb.edu> wrote in message news:Jt21tp.nGo@lugnet.com... (...) rectangle expanding into an empty rectangle in the bottom right corner of the YouTube play bar. Clicking this will allow you to enter full-screen mode. (Esc (...) (17 years ago, 15-Dec-07, to lugnet.technic)
| | | Re: Digicomp II
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| (...) understand how some of it works... What does the lower layer do? Is it just concerned with 2's complementing and clearing the accumulator? cheers, Alexander (17 years ago, 15-Dec-07, to lugnet.technic)
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Message is in Reply To:
| | Digicomp II
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| (...) Wow! I for one can hardly wait to see the video of this. And I would love to see more explanation and construction details too! cheers, Alexander (17 years ago, 10-Dec-07, to lugnet.technic)
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