16 Jul
2006
16 Jul
'06
8:35 a.m.
I'm not looking for a potted answer here - just ideas for where to look. Is ~28KHz a
common HSYNC frequency? seems too low for anything I've seen.
What else should I look at for a non-syncing monitor? USENET seems to indicate 48.8 KHz
HSYNC on these old SGI monitors (SGI employee posting),
so I'm not sure where the ~28 KHz is coming from- is this crystal or RC controlled?
There are about 9 boards in the graphics half, I suppose sync is generated
on the last one (in this case the DC4 display controller) - no crystals there.
Common failure on old framebuffers? any tips? tony?
16 Jul
16 Jul
9:59 a.m.
Scott Quinn wrote:
I'm not looking for a potted answer here - just ideas for where to look. Is ~28KHz a
common HSYNC frequency? seems too low for anything I've seen.
Hmm, I'd expect an SGI (or similar machine of its class) to be attempting
1024x768 at 60Hz non-interlaced minimum, so hsync somewhere around 50KHz.
What else should I look at for a non-syncing monitor?
Is it the monitor or the machine? For a monitor test I'd throw it on any old
PC and see what I could get out of it (wire up a sync combiner if the monitor
needs csync; easy to do)
USENET seems to indicate 48.8 KHz HSYNC on these old
SGI monitors (SGI employee posting),
Plausible, anyway.
I suppose it's just possible that you could do interlaced 1024x768 with a
28KHz signal, but it'd be hell on the eyes. Possibly that's the SGI's default
though if it can't detect what monitor you're plugging into it? (scratch that
idea if the outputs are BNC, but if the video's done over some form of
multi-pin connector, might it not need strapping in a certain way to indicate
display type?)
cheers
Jules
2:04 p.m.
I'm not looking for a potted answer here - just ideas for where to
look. Is ~28KHz a common HSYNC frequency? seems too low for anything
I've seen.
It might be, although it sounds low for a workstation monitor. TV HSync
is around 15.6kHz (different on the 2 sides of the Pond, but suprisingly
close!), The IBM MDA was around 18kHz. And so on.
For a non-interlaced monitor, the ratio of hyxnc to vsyn frequencies is
the total number of lines in the picture (including non-displayed lines
during the flyback time). For 2-way interlace, it's half the number of
lines, and so on.
This might give you an idea if the hysnc frequency is reasoanble. Is the
Vsync frequency reasonable (likely to be 10's of Hz -- 50Hz, 60Hz or
something like that). If it is, does the number of lines make sense based
on the resulution of the display.
What else should I look at for a non-syncing monitor?
USENET seems to
indicate 48.8 KHz HSYNC on these old SGI monitors (SGI employee posting),
That would be more like what I'd expect on a workstation.
so I'm not sure where the ~28 KHz is coming from-
is this crystal or
RC controlled? There are about 9 boards in the graphics half, I suppose
sync is generated
Almost certainly there's one master crystal oscillator that's digitially
divided down to produce all the video timing signals.
-tony
6734
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6734
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