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Forum Index : Microcontroller and PC projects : 240 x 144 resolution
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Geoffg Guru  Joined: 06/06/2011 Location: AustraliaPosts: 3194 |
Another reply that was getting of topic... The way that I got 240x216 resolution was by halving the video speed to get 240 pixels wide and and by drawing each pixel twice on two successive scan lines (216 pixels high). I have done some more experimenting and I can get 240 x 144 pixels (one pixel to three scan lines) but it looks distorted with the characters tall and thin (because each pixel is tall and thin). Also there are much less pixels to draw with. This seems a backwards step. I think that the confusion is because the Maximite pixels are not square. If we had square pixels then 400x240 or 240x144 would be fine. You are right when you said that the horizontal resolution of the Maximite does not match the typical pixel density of a VGA monitor - that is the issue and that is caused by the speed at which pixels are sent to the VGA screen. The problem here is that the Maximite does not have a VGA graphics system. It (mis)uses the SPI interface on the PIC32 chip to clock out the video and the SPI just cannot do everything that you would expect with a specialised graphics subsystem. Remember that this is a computer system that is entirely implemented within a $9 chip !! The current resolution of 480x432 and the resulting non square pixels was dictated by what I could get the SPI interface to do, it was not a considered decision. By halving the SPI clock speed we can get 240 pixels wide but the SPI does not allow a fractional adjustment of the clock's speed, which is what we need to get square pixels. There are some other tricks which I am investigating that might reduce the problem but I cannot hold out a lot of hope at this stage. I hope that this helps, Geoff Geoff Graham - http://geoffg.net |
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| JohnS Guru Joined: 18/11/2011 Location: United KingdomPosts: 3801 |
Could a different xtal be used for the PIC32 to do it? John |
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| Geoffg Guru Joined: 06/06/2011 Location: AustraliaPosts: 3194 |
Yes, but only by over clocking by about 30% Geoff Graham - http://geoffg.net |
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vasi Guru Joined: 23/03/2007 Location: RomaniaPosts: 1697 |
And it will require a heatsink?. Hobbit name: Togo Toadfoot of Frogmorton Elvish name: Mablung Miriel Beyound Arduino Lang |
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darthmite Senior Member  Joined: 20/11/2011 Location: FrancePosts: 240 |
Heya 
Geoff is going back to the source 
240 x 200 8 colours was the Oric1 / Atmos resolution. Was only 160 x 200 for the C64 but 16 colours. And the CPC464 that i am sure some of you have spend allot of your night was like C64 for the 160 x 200 and a 320 x 200 in 4 colours. But what is at best is that the MM is allot faster than all my lovely prehistoric machines 
Great work Geoff , and because your not finish with the Dev of this new MM. In case you don't know what to add , then ... polygon and filled polygon will be a good one. for ex: dim Ptsx(20) , Ptsy(20) .. fill the Ptsx and y data ... Polygon(Nb_Pts,Ptsx,Ptsy,external_color,internal_color,Fille d) and Polygon(Nb_Pts,Ptsx,Ptsy,external_color,,Empty) and Polygon(Nb_Pts,Ptsx,Ptsy,external_color,internal_color,XOR) .. NOT .. AND ... etc ... and ..... you see
The last point from the poly is automatically connected to the first one (or not) if you add the option ... I can continue like this up you fill the whole PIC32 but it will be for the next time 
Cheers. Theory is when we know everything but nothing work ... Practice is when everything work but no one know why ;) |
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| JohnS Guru Joined: 18/11/2011 Location: United KingdomPosts: 3801 |
I was wondering about a reduced clock rather than overclocking. Just a thought. John |
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