F-Cycles Posted July 23, 2013 Share Posted July 23, 2013 I have started to look to the video chip and especially the VDP Block Diagram. I don't have a real hardware and my tests are limited to be running in BlueMSX. So far, my test show that a single sprite can have a different color per scan line and a single sprite can be 16 pixels by 192. But that's not that interesting with the 32 sprites already available... unless to show a screen with 48 sprites - did anyone had ever done it? - (since 192 pixels height is 12 sprites and 4 sprites per line x 12 sprites = 48 sprites on screen). In fact, all values seem to be stored for each scan line... Which I am not sure it's the case on the real hardware for all values!? Because the VDP has 8 internal registers. Some of these registers may be connected directly to other gates to produce the desired results... That's my guess so far. I target especially the register which magnify the sprites (which does not need to read any values from the RAM to be effective). This bit could be directly connected via a line to a logic gate and as soon the bit toggle, it may produce a change in the circuitry... in my test, I place 2 sprites one on the left side of the screen and one on the right side of the screen. The distance between the two was $D0 which is 208 pixels... which give about 138.6 T (CPU) clocks in between the two (enough for the few instructions needed). I then attack the register 1 toggling the bit. The result is that I see one scan line show the 2 sprites magnify by 1x and next scan line magnify by 2x and so on (few scanline has double 1x or 2x), as I did not try to be in sync with the HSYNC. I pause the emulator a couple of time and never notice for the same scan line a different result for the 2 sprites. I would like to know if someone has done some research about that MAG bit or the SIZE bit? Thanks Best Regards, Quote Link to comment Share on other sites More sharing options...
+5-11under Posted July 23, 2013 Share Posted July 23, 2013 Very interesting. Got any screen shots or code or ROM files to check out? Quote Link to comment Share on other sites More sharing options...
F-Cycles Posted July 23, 2013 Author Share Posted July 23, 2013 Very interesting. Got any screen shots or code or ROM files to check out? Hum.. Sorry I post my reply to the thread... 'Fun with VDP status register' I try to delete it after posting it.. so I could put it here. But, well.. at least it kind of related with the topic of video processor. Quote Link to comment Share on other sites More sharing options...
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