VRAM: Difference between revisions
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[[File:Aes_cxk5814.jpg|thumb|One of two CXK5814 2KiB RAM chips used for the upper zone of the VRAM ($8000~$87FF) on a AES system]] | [[File:Aes_cxk5814.jpg|thumb|One of two CXK5814 2KiB RAM chips used for the upper zone of the VRAM ($8000~$87FF) on a AES system]] | ||
The NeoGeo has 68KiB (physically 64KiB + | The NeoGeo has 68KiB (physically 64KiB + 4KiB) of VRAM organised as 16 bits words, which is used to store [[Sprites|sprite]] attributes and the map for the [[fix layer]]. Contrary to other systems, the VRAM here '''does not contain actual graphics'''. | ||
It isn't mapped in the [[68k]]'s address space. The only way to read and write to it is by using 3 [[Memory mapped registers]]. Every address points to a word, not a byte. | It isn't mapped in the [[68k]]'s address space. The only way to read and write to it is by using 3 [[Memory mapped registers]]. Every address points to a word, not a byte. | ||
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|$8600 | |$8600 | ||
|? | |? | ||
| | |Dual sprite display lists | ||
|} | |} | ||
Revision as of 14:24, 30 May 2011
VRAM stand for Video RAM.
The NeoGeo has 68KiB (physically 64KiB + 4KiB) of VRAM organised as 16 bits words, which is used to store sprite attributes and the map for the fix layer. Contrary to other systems, the VRAM here does not contain actual graphics.
It isn't mapped in the 68k's address space. The only way to read and write to it is by using 3 Memory mapped registers. Every address points to a word, not a byte.
- VRAM_ADDR ($3C0000) sets the VRAM address
- VRAM_RW ($3C0002) is the data to read or write
- VRAM_MOD ($3C0004) is the signed value added to the VRAM address after a write
Memory map
| Start | End | Description |
| $0000 | $6FFF | SCB1 |
| $7000 | $7FFF | Fix map |
| $8000 | $81FF | SCB2 |
| $8200 | $8400 | SCB3 |
| $8400 | $8600 | SCB4 |
| $8600 | ? | Dual sprite display lists |
VRAM can be modified at any time, even during active display.