Ed, since each hi-res page has 192 lines, and since the monitor
you are using is only capable of approximately 60Hz vertical
deflection and approximately 15kHz horizontal deflection, the
only way to get more than 260 or so lines (including vertical
blanking interval) is to interlace.
By that, I mean that all the odd-numbered lines of both screens
are displayed first (the first 192 active lines), then all the even-
numbered lines of both pages are displayed between the odd
lines of the first field. This will create an image of screen 1
over screen 2, each screen containing 192 active lines.
This is the way that "ordinary" TV gets about 500 lines, and
is the only way that a TV-standards display can do so.