Composite video output from ST

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2 total messages Started by John Purbrick Thu, 20 Mar 1986 20:06

#237

Author: John Purbrick
Date: Thu, 20 Mar 1986 20:06

12 lines
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The 1040ST, and now the 520ST, offer composite video output compatible with
normal monitors, or rf-modulated for TVs. There were a few questions here
a while back about how the ST reads its video memory to drive the display
without slowing down the processor (answer--video reads are done while the 
processor isn't using the bus, mostly) but now Atari has come out with an
additional video output, which can't be compatible with the "normal"
display drive as that is 70Hz, non-interlaced and regular monitors are
60Hz, interlaced. Does the new 60Hz display use the same technique as
before, using the bus alernately with the processor, so all three of them
are banging away? This makes it seem like there would be frequent bus-
contention, especially between the 60Hz and 70Hz accesses. Is there some
kind of magic that makes this less of a problem?

Re: Composite video output from ST

#250

Author: John Purbrick
Date: Sat, 22 Mar 1986 22:44

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Since noone has answered my question yet, here it is for anyone who's 
interested (the question was how do the new ST's generate 60Hz and 70Hz
video simultaneously): 

In fact they don't. The 70Hz monitor, if used, is detected and causes the
ST to generate the appropriate video signals. Otherwise 60 Hz (only) is
generated, at least I think this is what happens.

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