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Originally Posted by kovacm
@zero
So 68000 in CPS never read graphics or sound data from ROM but only "order" to video and sound hardware what and how they should draw/play. This is somehow similar to e.g. how Amigas 68000 setting custom chips (blitter, agnus, paula...)?
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Yes, that's right. It's like how once you have copied graphic data for a sprite into RAM on the Amiga, all you need to do to display it is to set the sprite hardware registers up with a pointer to the data and where to display it. The hardware then reads and displays that data itself, the CPU doesn't have to manually copy it to the screen bitmap.
It's the same with sound. You just tell the hardware which bit of RAM to read the sample data from, what pitch and how long to play it for, and it does all the actual reading of data for you.
The main difference with the CPS hardware is that all the graphics and sound are in ROM. There is no need to copy them to RAM, they can be read directly from ROM by the graphics hardware. On the Amiga you have to load the graphics from disk into RAM, so you need a lot of RAM.
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192 KB VRAM in CPS is used to compose background layer?
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It doesn't use bitmaps if that's what you mean. The background layers are tile maps, which are stored in VRAM. So rather than actual graphics, it's just a 2D array of tile numbers. The hardware knows where in ROM to look for each tile number.
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Anyway, quite clever system  how much did cost ROM vs RAM back in 80s and 90s?
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ROM was a lot cheaper. In arcade systems cost wasn't such a big issue though. The ROM is more like a floppy disk on the Amiga - most games don't write to floppy, it's effectively read-only.
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I found how Metal Slug for NeoGeo compose display (somebody spread graphics to layers):
[ Show youtube player ] - but I am not sure how much NeoGeo is different from CPS...
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It's similar but more advanced. On the NeoGeo there are no background layers, you just use sprites to make the background. And it has a few more features like sprite scaling and more of them compared to CPS. And it supports much larger ROMs.