Video Interface: Difference between revisions
→0x0440 0020 - VI_H_SYNC_LEAP: by the evidence, this must be how LEAP is implemented
(→0x0440 0020 - VI_H_SYNC_LEAP: Mention serration...) |
(→0x0440 0020 - VI_H_SYNC_LEAP: by the evidence, this must be how LEAP is implemented) |
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'''Extra Details:'''
: LEAP_n specifies an alternate scanline length for one scanline during vsync. Values larger than H_SYNC specify the length of the second scanline of vsync. Values smaller than H_SYNC specify the length of the first scanline of vsync and have a variety of undesired side effects, such as skipping one hsync entirely or leaving csync erroneously high for one whole scanline. Serration changes these effects subtly.
: Specifically, a counter is started at the start of vsync. When that counter is equal to LEAP_n, the VI starts or restarts the second scanline of vsync without changing the status of the csync bit.
: The default PAL values of LEAP, LEAP_A, and LEAP_B appear to be responsible for adding PAL's nominal "one extra chroma period per 625 scanlines emitted".
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