At 11:35 25.07.2000 -0700, you wrote:
>Could someone write an overview of how VDEL is actually used in a kernel as
>a vertical positioning system for me in such a way that I can just
>paraphrase it into a voiceover? It seems that would be the easiest way to
>do it.
OK, lets define the situation:
Each player graphics has two registers GRP0-A and GRP0-B, GRP1-A and GRP1-B.
The VDEL register for a player decide whether the A or the B register gets
used for display in a given line.
The graphics from the A register gets copied into the B register when
some data gets written into the A register of the other player.
Therefore in a double scanline kernel you would in every scanline:
check if the player has to be displayed.
if so, check which line of graphics has to be displayed ...
and write that out.
if not, write out a blank graphics byte.
You alternate between players in every scanline.
Now lets have a look at two double scanlines. All four graphics registers are
set to $00. GRP0 gets handles in the first scanline and GRP1 in the second
scanline of each double scanline set:
If you want to display player0 in line 3, you would turn off it's VDEL
register and set it's verical position counter to the second line-set.
If you want to display player0 in line 4, you would turn on it's VDEL
register and set it's verical position counter to the second line-set.
If you want to display player1 in line 3, you would turn on it's VDEL
register and set it's verical position counter to the first line-set.
If you want to display player1 in line 4, you would turn off it's VDEL
register and set it's verical position counter to the second line-set.
>I'm including a file here which is a shockwave flash that is supposed to
>illustrate a 4-bit polynomial counter.
That one didn't make it.
>I would like to expand on this diagram to show how the TIA drives the
>speaker with this type of counter, and how it performs sprite positioning
>(via coarse and fine registers) in combination with the binary/decimal ->
>poly value code.
Sorry, I can't help you here. Did anyone here ever figure out how the
poly counters relate to the TIA register?
Ciao, Eckhard Stolberg
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