VGA Video Card Project
Jorge Chamorro Bieling, 18 de Febrero, 2006
home
-Whatever is happening in the 6502's address and data bus can be "seen" in any slot of the Apple II.
-The slots are a good place to plug in in order to monitor the processor's address and data buses.
-Therefore a card that keeps a copy of mainboard's RAM contents can be easily designed.
-By properly watching the bank-select softswitches, the card can duplicate the auxiliary RAM contents too.
-A live copy of all the Apple II memory's data in the card's own RAM can be easily scanned in order to generate the video signal at a VGA scan rate that will allow you to connect the Apple II to a modern, more readily available VGA CRT or LCD display.
-There's no need to modify nor depend upon the Apple II's onboard video generator circuit.
-This is not a video converter, it is a video generator that emulates the Apple II's onboard video generator.
-With some added effort, can be made programmable and generate additional more convenient linear mapped or higher resolution or deeper color or enhaced video modes, at the cost of compatibility.
This is the block schematic of the idea :
Things
that can easily be done in a design like this:
100% Apple II compatible video modes:
- See both HGR pages side by side at the same time
- See both text pages side by side at the same time
- See all of them at the same time in a mosaic image: 2 HGR + 2 TEXT screens.
- Programable vertical and/or horizontal blanking/sync interrupt sourcing.
- Works equally well for PAL and NTSC Apple IIs.
New (incompatible) possible video modes:
- More than two HGR pages.
- Easily attainable 320*192 quite "compatible" monochrome HGR mode.
- Map all the Apple II's memory map, up to 96k, pixel by pixel, to a 1024*768 bitmap : every bit is seen as a single pixel : watch your Apple II memory activity live on-screen !
- Move TEXT or HGR pages to more convenient areas of the memory map.
- TEXT modes with more than 80Columns*24Rows.
- Colored text.
- Higher resolution "HGR" modes.
- Graphics mode bitmaps and text pages can be made linear for easier/faster addressing.
- etc.
Also:
- This card can be made "transparent", this means that even if it sits in one slot you could still plug in the same slot another card at the same time, as the circuit does not use any of the memory map addresses reserved for that slot : it can be designed in such a way that you don't loose any slot.
Interesting readings:
- Apple II Tech. Note #3"Double High-Resolution Graphics"
- USPAT#4578673 (Franklin Computer Corporation) Video color generator circuit for computer.
- USPAT#4786893 (Apple Computer, Inc.) Method and apparatus for generating RGB color signals from composite digital video signal.
- USPAT#4631692 (Video 7 Incorporated) RGB interface.
- USPAT#4533909 (Apple Computer, Inc.) Computer with color display.
...
Update 20/FEB/2006 •• csa2 thread ideas:
aiiaddict -> put as much as possible in sopc (fpga/cpld ?).
Alex Freed -> No need to use a dual-ported RAM.
sicklittlemonkey -> "windowed" graphics memory for new video modes
sicklittlemonkey -> easy LoRes(GR)-like pixel representation.
me -> this design will work for the Apple IIc/IIc+ too !
100% Apple II compatible video modes:
- See both HGR pages side by side at the same time
- See both text pages side by side at the same time
- See all of them at the same time in a mosaic image: 2 HGR + 2 TEXT screens.
- Programable vertical and/or horizontal blanking/sync interrupt sourcing.
- Works equally well for PAL and NTSC Apple IIs.
New (incompatible) possible video modes:
- More than two HGR pages.
- Easily attainable 320*192 quite "compatible" monochrome HGR mode.
- Map all the Apple II's memory map, up to 96k, pixel by pixel, to a 1024*768 bitmap : every bit is seen as a single pixel : watch your Apple II memory activity live on-screen !
- Move TEXT or HGR pages to more convenient areas of the memory map.
- TEXT modes with more than 80Columns*24Rows.
- Colored text.
- Higher resolution "HGR" modes.
- Graphics mode bitmaps and text pages can be made linear for easier/faster addressing.
- etc.
Also:
- This card can be made "transparent", this means that even if it sits in one slot you could still plug in the same slot another card at the same time, as the circuit does not use any of the memory map addresses reserved for that slot : it can be designed in such a way that you don't loose any slot.
Interesting readings:
- Apple II Tech. Note #3"Double High-Resolution Graphics"
- USPAT#4578673 (Franklin Computer Corporation) Video color generator circuit for computer.
- USPAT#4786893 (Apple Computer, Inc.) Method and apparatus for generating RGB color signals from composite digital video signal.
- USPAT#4631692 (Video 7 Incorporated) RGB interface.
- USPAT#4533909 (Apple Computer, Inc.) Computer with color display.
...
Update 20/FEB/2006 •• csa2 thread ideas:
aiiaddict -> put as much as possible in sopc (fpga/cpld ?).
Alex Freed -> No need to use a dual-ported RAM.
sicklittlemonkey -> "windowed" graphics memory for new video modes
sicklittlemonkey -> easy LoRes(GR)-like pixel representation.
me -> this design will work for the Apple IIc/IIc+ too !