[GreenKeys] [External] Re: Hal ST-6 using it in modern times

[Jones, Douglas W]

From: Dave Horsfall [dave at horsfall.org] -- Sunday, March 22, 2020 4:30 PM

On Sun, 22 Mar 2020, John, W9DDD wrote:

> You had 525 lines?  We only had 405 of them back in Merry Olde England...

I thought it was 522, but we got that using interleaving.  So each (half) frame only had 261 lines, but successive (half) frames were bounced vertically by half the spacing between the lines within each (half) frame.  To get 525, you have to assume alternate (half) frames had 262 and 263 lines.  Lovely, but it worked.  The jitter in the alignment of successive (half) frames was done by coming out of "ultrablack" at the start of one (half) frame but in mid-scan-line on the next (half) frame.  Ultrablack was the voltage level on the video signal used for syncing the horizontal and vertical sawtooth oscillators.  Additional details included the front porch and back porch on each sync signal, providing a black frame around each frame of the image.

              Doug Jones
              jones at cs.uiowa.edu

(also old enough to remember all those tobacco ads)