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#1 |
Registered User
Join Date: Dec 2010
Location: United Kingdom
Posts: 156
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Changing video port master clock
Okay, anyone who's seen my posts lately knows I've been looking into getting smooth scrolling, V-Sync locked output at both 50hz and 60hz on my CD32. On my PAL machine I've noticed that when it's set to 60hz NTSC the vertical sync comes out as 59.28hz. This is too far out of spec for my TV to get a V-sync lock and so it stutters.
I was chatting to a friend about this and he just e-mailed me with some interesting information:- Just been digging around (reading the Amiga Technical Reference Manual if you must know ![]() So, is there anything in this or is it barking up the wrong tree? I wouldn't have a clue where to start with what hardware mod was required, but I am very interested. |
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#2 |
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Join Date: Jul 2003
Location: Helsinki / Finland
Age: 43
Posts: 9,906
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It's basically what a genlock does. This might not work with non os-friendly software, but I haven't tried it myself.
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#3 |
Registered User
Join Date: Dec 2010
Location: United Kingdom
Posts: 156
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Yeah we were thinking Genlocks, but I never owned one, I've no idea how they work. Can anyone elaborate further?
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#4 |
Registered User
Join Date: Jan 2008
Location: United Kingdom
Age: 46
Posts: 733
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Hi,
Using a 28.63636 MHz oscillator and feeding it into XCLK (pin 1) should work. Connect XCLKEN to ground with a 100 ohm resistor to enable this mode. 28.63636 MHz oscillators are available as they are 8x the NTSC colour burst frequency, commonly used with video devices. The slight difference in the Vsync timing will be down to the difference between the 28.63636 MHz crystal of an NTSC and the 28.37518 MHz used on PAL machine. I don't have a copy of SMPTE 170M here but I remember you multiply and divide the reference clock many times to make the line/field sync timings from the one, tight, reference clock. There are some details on Genlocks in the Amiga developer CD 2.1 Ian |
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#5 |
Registered User
Join Date: Dec 2010
Location: United Kingdom
Posts: 156
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Ah so we were thinking on the right lines at least. This could be built into a SCART cable then? Sadly I've no soldering/hardware construction skills so I guess the project will forever remain just an idea, especially as I seem to be in the minority when it comes to noticing stuttery scrolling anyway!
If anyone fancies constructing this cable for me I will reward you financially and with a spot of honour on my amazing website, lol ![]() |
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