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YPS
Registered: Oct 2012
Posts: 5 |
$39FF instead of $3FFF as alternative bit-pattern for open border
I thought it's ALWAYS the last byte of the VIC-bank, that is displayed in the open border area (upper and lower).
But with "Extended Backgroundcolor Mode" on, the value of $39FF (of the VIC-Bank) is shown instead.
A usecase might be, that you can use all spritepointer together with the highest videoram - with "Extended Backgroundcolor Mode" off, the pointer of sprite 7 would be displayed as garbage in the border. Of course, there are solutions to avoid this, but maybe someone else find this usefull. |
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Radiant
Registered: Sep 2004
Posts: 639 |
This is documented in the VIC article (section 3.7.1) for those who want to know more about the mechanism behind the "ghost byte". |
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JackAsser
Registered: Jun 2002
Posts: 1987 |
Quote: I thought it's ALWAYS the last byte of the VIC-bank, that is displayed in the open border area (upper and lower).
But with "Extended Backgroundcolor Mode" on, the value of $39FF (of the VIC-Bank) is shown instead.
A usecase might be, that you can use all spritepointer together with the highest videoram - with "Extended Backgroundcolor Mode" off, the pointer of sprite 7 would be displayed as garbage in the border. Of course, there are solutions to avoid this, but maybe someone else find this usefull.
A classic use case is to avoid having the IRQ-pointer ($ffff) end up in the idle-pattern...
A bit off topic:
But if that still is a problem, like it was for me one time, I resorted to KERNEL-ROM pointers and put $00 in $ffff (RAM) since the VIC always read RAM but the CPU reads ROM in that case. |
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Radiant
Registered: Sep 2004
Posts: 639 |
Quoting JackAsserA bit off topic:
But if that still is a problem, like it was for me one time, I resorted to KERNEL-ROM pointers and put $00 in $ffff (RAM) since the VIC always read RAM but the CPU reads ROM in that case.
Or just put the IRQ handler in zeropage. ;-) |
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Peiselulli
Registered: Oct 2006
Posts: 81 |
Or use the NMI instead .. |
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Oswald
Registered: Apr 2002
Posts: 5017 |
or jmp abs on zeropage.. |
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algorithm
Registered: May 2002
Posts: 702 |
or in the displayed area, change $ffff to your hearts content and then when in the non visible area, change it back to the irq hi pointer. Can be useful in particular if you are not planning on exiting irq during the ghostbyte displaying. |
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mrmedic
Account closed
Registered: Jul 2007
Posts: 4 |
you can trick the vblank d012 into thinking its no at the end and have full screen.
you have to put a sprite on the end , and it opens it every 12 lines. borderless c64 screen. i done it in a demo for s xpress in grimsby i used the sprites from hawkeye ( that one with the hawns ) it ran across the screen jumping over the scrollers at random times. |
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JackAsser
Registered: Jun 2002
Posts: 1987 |
Quote: you can trick the vblank d012 into thinking its no at the end and have full screen.
you have to put a sprite on the end , and it opens it every 12 lines. borderless c64 screen. i done it in a demo for s xpress in grimsby i used the sprites from hawkeye ( that one with the hawns ) it ran across the screen jumping over the scrollers at random times.
Wait! What?! (Oo) |
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chatGPZ
Registered: Dec 2001
Posts: 11092 |
*plop* |
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Radiant
Registered: Sep 2004
Posts: 639 |
LOL! |
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