I would love to see this wonder book of yours -- what is the title?
"Graphics Primer for the IBM PC".
I also would definitely like to see the interlaced listing, because that's the only thing I have not been able to see any use for. You would think that you can use interlaced mode to get 400 interlaced lines, but when I do it, I just get alternating pages on the same 200 lines (which makes interlaced mode worthless). Working with Andrew Jenner, we determined that IBM did not implement the interlaced functionality properly.
It's just a short program that turns the interlace mode on and fills the screen with As. You will also get some snow since it's writing directly to the video memory in 80-column text mode. There's four different settings for the interlace register. A value of 0 or 2 just produces a noninterlaced picture. 1 (probably what you tried) causes both pages to repeat the same information, and 3 produces a proper 400-line display.
5 'interlaced text
10 screen 0,0
20 width 80
30 cls
40 out &h3d0,8: out &h3d1,3
50 def seg=&hb800
60 for i=3 to 49
70 for j=0 to 79
80 poke 160*i+2*j,65
90 next j
100 next i
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