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Oswald
Registered: Apr 2002
Posts: 5017 |
Screen with no Badlines
Hello there!
I know it's possible to have a screenmode with no bad lines at all, graphics are not displayable, but sprites are visible in this one. Once I've coded it but now I totally forgot how it was done.. some d011 fiddling at the start of the bottom border.
Can anyone tell me how to achive this ? Whats the theory ? |
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SIDWAVE
Account closed
Registered: Apr 2002
Posts: 2238 |
Interresting stuff!
I'd sure like to see that EGMOS thing |
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Barfly
Registered: Jan 2002
Posts: 4 |
Actually you can do this trick even without opening the upper/lower borders...
.Barfly |
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bOOZElEE
Registered: Dec 2002
Posts: 34 |
@ rambones: scpu owner?
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WVL
Registered: Mar 2002
Posts: 886 |
Quote: Actually you can do this trick even without opening the upper/lower borders...
.Barfly
how? you have to avoid the VIC starting drawing the border, else the whole screen will flush!
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Krill
Registered: Apr 2002
Posts: 2839 |
yeah. maybe barfly meant just a full-screen fld to scroll out all badlines =) but that would mean d011 writes at least every 6 lines. |
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VIC
Registered: Aug 2003
Posts: 73 |
Quote: how? you have to avoid the VIC starting drawing the border, else the whole screen will flush!
*draw, draw, draw* |
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Ninja
Registered: Jan 2002
Posts: 404 |
I hope I am not spoiling Barfly's fun, but sharing knowledge rules ;)
Badlines can just occur if "Display Enable" was set in line $30 for at least one cycle. So, make sure that it is cleared during line $30, and the it is set before $33, so that the border-flip-flops will behave like having a "normal" screen.
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Ninja
Registered: Jan 2002
Posts: 404 |
Example code:
SEI
loop3:
LDA #$2F
loop1:
CMP $D012
BNE loop1
BIT $D011
BMI loop1
LDA #$0B
STA $D011
LDA #$31
loop2:
CMP $D012
BNE loop2
LDA #$1B
STA $D011
BNE loop3
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WVL
Registered: Mar 2002
Posts: 886 |
hmmm..... okay, this should work too :) but basically the problem is the same. Whether you enable the screen before line $33 or open the border around $fa, it does not matter...
timing-wise they are both equally simple [or hard if you want a flexible irq over it], plus you get a free open upper+lower border :) |
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Ninja
Registered: Jan 2002
Posts: 404 |
Of course, they are pretty similar. It was just the answer to the question "how?" :) |
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