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From: Crown (all posts)
Date: 1998-05-21
Subject: Re: TED timing

Hi there,

>The last value might change if you move the screen origin. The video chip seems
>to switch to 1MHz mode on raster line 0, even if the graphics begins at a later
>line, like line 4 in the measurement above. Moving the screen down would
>perhaps decrease the amount of free cycles.

If you write $0 into the Y scroll part of $ff06, then line 0 will be a bad line, and the color memory will be fetched, and line 1 will be also a bad line, here will be the character image code will be fetched. This is why it falls back at line 0.
If you scroll up at least one line than normal, then there will be
2 more bad lines on screen, so the amount of the free cycles will decrease.
Also if you open up the borders, this will turn a lot of border lines into bad, and gfx or normal screen lines.

>The addresses of the "?" and "r" cycles need to be revealed. They must In line3 and in all ? cycles the memory at $ffff is read. If you scroll the screen downwards and stay in 25 line mode, this value will be displayed as graphics. This shows, that there is two separate part inside TED,
one which is responsible for fetching the color and character attributes,
and one which is responsible for fetching the bitmap data.

Tibor Biczo / Crown of GOTU