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PostPosted: Wed Sep 10, 2014 12:22 pm 
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Joined: Sun Sep 19, 2004 11:12 pm
Posts: 19246
Location: NE Indiana, USA (NTSC)
Some values for Steepler's Dendy famiclone in Clock rate are guessed from the "Dendy Chronicles" video, which was made with a later model NOAC-based Dendy system using T1818P (pic), 6561A (pic).

Eugene.S wants to confirm this on the UA6527P CPU and UA6538 PPU used in the original Dendy. Here is Eugene's emphasis bits result, showing that red and green are swapped just as on the PAL NES. He asked me to pass on to the forum that he seeks test ROMs for these behaviors of the 6538:
  • Overscan color. Is it forced black or otherwise? Does it differ at the sides vs. at the top and bottom? If it's forced to black, does the black protrude 2 pixels into the picture like it does on PAL NES?
  • Behavior of OAM DMA during forced blanking. The official PAL NES refreshes OAM outside lines 241-260 even if rendering is disabled, causing OAM DMA to fail except during the start of vblank. The Dendy has its screen update period near the end of vblank (lines 291-310) for maximum compatibility with cycle-counting interval timers in Japanese mappers such as FDS, VRC, and FME-7, and I wonder if it too does some sort of OAM refresh during its post-render scanlines (240-290).


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