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

[Nick England]

525 lines per frame in the US. 485 visible lines.
Each field was 262-1/2 lines of which 242-1/2 were visible (vertical
blanking interval was 20 lines)
If you didn’t generate the equalizing and serration pulses in the vertical
interval correctly, the interlace would be very slightly off. I could tell
because I really knew this stuff way back when I designed a computer
graphics display system that was dead on spec.
NTSC. Never Twice the Same Color

625 lines outside the US for PAL and SECAM.

Nick


On Sun, Mar 22, 2020 at 6:10 PM Jones, Douglas W <douglas-w-jones at uiowa.edu>
wrote:

> 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)
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-- 
Nick England K4NYW
www.navy-radio.com
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