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Chesler
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Re: PROGRAM
Chesler   1/8/2014 3:50:08 PM
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What am I doing debugging/reverse engineering this?
Since N is set to N-1 before the loop, I'm thinking F was initialized to N, not to 1.

I remember being amazed at how quickly the answer came back (relative to 110 baud -- but a state-of-the-art TI-30 of the same vintage has noticable lag coming back with a trig value) so maybe I was trying to be clever and save a multiplication.

 

David Ashton
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Re: Working!
David Ashton   1/8/2014 2:40:41 PM
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@Chesler....no problem, I had lots of fun with it.  (If MS had not updated everything I'd still be quite happy with DOS and BASIC and Wordstar :-)

In your original program, if Nwas input as 1, it would have got 1 subtracted from it first, and you would have got an endless loop.  Mine can cope with 1 but not 0 or negative Ns.  

I remember being taught that unconditional jumps like GOTO 60 were a no-no, and to use DO WHILE  or FOR N = x TO y instead.  Good point.

I did a FORTRAN course once and put and endless loop in a program, I got presented with a 2 inch high stack of paper and a very stern talking-to from the computer centre manager when I went to collect my printout.  We all have to start somewhere.....

Chesler
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Re: Working!
Chesler   1/8/2014 10:32:25 AM
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Thanks David Ashton.
I think Y-512 may have been my account on the timeshare.
No idea what was supposed to be at lines 40 and 50 (presumably one of them initialized F), or why they didn't save to the tape.
Line 85 :-)  I guess the day before I'd written my first endless loop!

betajet
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Re: Working!
betajet   1/8/2014 9:39:11 AM
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Now you just need to punch the updated program onto paper tape and you're done!

David Ashton
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Working!
David Ashton   1/7/2014 11:22:33 PM
How about that!  You can still get good old GWbasic from here

http://gwbasic.webs.com/download.htm

or here, which has manuals as well

http://www.gw-basic.com/downloads.html

Pretty good value for 60K (yes K not M) of program!!

I got the program working -  as I thought, I had to initialise F and get the line numbers right for the jumps, but then it does work:

10  REM INPUT N, OUTPUT N!

20  PRINT "INPUT THE NUMBER THAT YOU WANT THE FACTORIAL OF"

30  INPUT N

35  F=1

70  IF N=1 THEN 100

80  F=F*N

85  N=N-1

90  GOTO 70

100  PRINT F

110  END

It only works up to N=30-something then it overflows.

Thanks guys, have not had this much fun in years!

 

David Ashton
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PROGRAM
David Ashton   1/7/2014 10:36:42 PM
I decoded the whole thing (no, not too much time on my hands, just a boring job) and got

10  REM INPUT N ; OUUTPUT N! BY Y-512

20  PRINT "INPUT THE NUMBER THAT YOU WANT THE FACTORIAL OF"

30  INPUT N

40  N=N-1

70  IF N=1 THEN 100

80  F=F*N

90  GOTO 60

100  PRINT F

110  END

I can see how it is supposed to work but a couple of things here
  • in line 80 variable F is not initialised, maybe that machine initialised unknown variables to 1?
  • line 90 jumps back to line 60 which does not exist, probably should be line 40

If the above is true then it should work, multiply N by itself N times.

I don't have a BASIC machine to run it on, does anyone?

betajet
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Re: scanner?
betajet   1/7/2014 1:38:36 PM
Oooh!  Even parity!  (More to come)

First line looks like:

10  REM INPUT N ; OUUTPUT N! BY Y-512

A good reference for an ASCII table and paper tape format is the DEC PDP-11 Peripherals Handbook, which is actually available at bitsavers.trailing-edge.com.  It's 28 MB, but all gold :-)

Page B-4 has an ASCII table in octal, which is the easiest way to decode paper tape.

Page B-5 shows how the bits are punched onto paper tape.  Bit 7 (MSb) is even parity on your tape, so ignore it.

Edit: You can also find a good example of paper tape and an ASCII table at Wikipedia.  However, Wikipedia's table is better suited for decoding hexadecimal.

 

rfindley
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Re: scanner?
rfindley   1/7/2014 12:40:03 PM
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A single LED (point light source) will cast an image through the holes that expands the farther you go from the tape.  Just move the photodiodes back an inch or so from the tape, to where the projected dot spacing matches the photodiode spacing.

Chesler
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Re: scanner?
Chesler   1/7/2014 12:04:36 PM
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h__p: //www.flicker.com/photos/chesler/11812689353



Max The Magnificent
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Re: scanner?
Max The Magnificent   1/7/2014 11:49:33 AM
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@Chester: For what it's worth, here is what the paper tape looks like:

Hi David -- I think you were trying to include a link to the image of your short paper tape program on Flickr, but for some reason it's not appearing -- if you email me the image I will make it available to folks.

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