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41 lines
1.4 KiB
Plaintext
41 lines
1.4 KiB
Plaintext
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VDP timing for an NTSC Genesis in display mode 5.
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Version 0.4 (11/29/00)
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by Charles MacDonald
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WWW: http://cgfm2.emuviews.com
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Unpublished work Copyright 2000 Charles MacDonald
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Description 32-cell 40-cell
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----------------------------------------------------------------------------
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Range 00-93, E9-FF 00-B6, E4-FF
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Display area 00-7F 00-9F
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V counter increment 84, 85 A4, A5
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V-blanking in 86, 87 A7, A8
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V-blanking out 86, 87 A7, A8
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H-blanking in 93, E9 B2, E4
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H-blanking out 06, 07 06, 07
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Comma seperated values show the H counter value before an event occurs,
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and then the H counter value immediately after.
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These values shouldn't be considered 100% accurate, they are probably
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off by one or two.
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Each H counter unit is equivalent to two pixels.
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The gaps at 93-E9 and B6-E4 are where the H counter 'jumps' ahead.
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The H counter will never actually be set to the values 94-E8 or B7-E3.
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Perhaps this is the horizontal retrace period.
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Interestingly enough, the timing values for the 32-cell display mode
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are identical to that of the SMS.
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It would appear that in 40-cell mode, the horizontal blanking period
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is shorter as the active display period takes more time.
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The V-blanking flag can also be forcibly set by disabling the display
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through bit 6 of register #1.
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