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  • Joined: 31 Oct 2007
  • Posts: 847
  • Location: Estonia, Rapla city
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SMS video output levels
Post Posted: Thu Oct 22, 2015 11:58 am


And today I finally got the SMS levels checked out. Good chuck went into debugging my flashing hardware which turned out to be faulty in the end.

I got measuremests from SMS1, SMS2, MD1 and MD2.

MD1 and 2 produced same results, SMS1 and 2 I had a bit of different measurement points. The usual point at voltage divider gave huge DC offset on SMS2 and I couldn't do measurements properly because of it so I measured the VDP output instead.

Here's the measurements for MD1 and 2 :

mV, ratio, RGB
0, 0.000, 0
368, 0.387, 99
604, 0.634, 162
952, 1.000, 255

SMS1 :

mV, ratio, RGB
0, 0.000, 0
324, 0.354, 90
620, 0.677, 173
916, 1.000, 255

SMS2 :

mV, ratio, RGB
0, 0.000, 0
364, 0.350, 89
720, 0.684, 174
1052, 1.000, 255

MD1+2 : 0, 99, 162, 255
SMS1 : 0, 90, 173, 255
SMS2 : 0, 89, 174, 255
Linear : 0, 85, 170, 255

Note that the MD measuremests DO NOT match any of the MD native mode output, there is some analog trickery going on or there's separate DACs used for SMS mode output.

Here's the test ROM (it is big because I hacked one game I have been sloooowly working on) : http://www.tmeeco.eu/SMS/COLOR.SMS

MD measurements found here : http://gendev.spritesmind.net/forum/viewtopic.php?f=22&t=2188
MD2SMSmodeRamp.jpg (371.16 KB)
MD2SMSmodeRamp.jpg
COLOR.rar (18.67 KB)

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Post Posted: Thu Oct 22, 2015 12:47 pm
Should you use gamma correction for the voltage to RGB conversion? My feeling is that TV colours are typically brighter than linear, even if the TV brightness and contrast is sensibly reduced from defaults.
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  • Joined: 31 Oct 2007
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Post Posted: Thu Oct 22, 2015 2:28 pm
When you apply gamma to that you apply it on top of what your video card and/or monitor alerady applies to the video out, making things worse.
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