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From: rick@mips.UUCP (Rick Frazier)
Newsgroups: net.micro.amiga
Subject: Re: flicker
Message-ID: <585@mips.UUCP>
Date: Mon, 28-Jul-86 11:34:00 EDT
Article-I.D.: mips.585
Posted: Mon Jul 28 11:34:00 1986
Date-Received: Tue, 29-Jul-86 01:55:39 EDT
References: <829@edison.UUCP>
Organization: MIPS ... where RISC is a way of life
Lines: 78

> I'm interested in doing a feasability study on circuitry
> to suppress the flicker.  I am not an electronics
> expert by any means but I have enough knowledge to at least
> not be too intimidated.
> 
> I realise one solution to the problem is a high persistence
> phosphor monitor but as they are quite expensive a circuit
> approach might be just as cost effective and possibly have
> other benefits such as a possibility of reducing the load
> on the processor.  Also, prices on monitors have been
> dropping relatively slowly compared to prices on semi-conductors
> thus a circuit solution can't help but look even better
> as time goes by.
> 
> It seems that one solution is a scan converter which
> will change the interlaced mode to a non-interlaced mode that
> updates at the required 1/60 of sec.  As I still have some
> warranty left on my machine, I am not prepared to open it up
> so have been left to reading the Hardware reference manual
> which doesn't get down to the nuts and bolts level.
> 
> From my reading, however, I noticed that one of the custom
> chips has 3 4-bit (R-G-B) outputs.  My surmise at this point
> is that these outputs are the results of the video sweep.
> I would expect that these outputs then travel to the
> monitor drive circuitry.  It should be possible
> to capture this output in video DRAMs ala. the TI dual
> port chip and save an entire screen (both scans).
> have to be in the RGB circuitry.  The $64,000 question is if
> I break the link in the RGB circuitry and somehow arrange that
> it re-injects a non-interlaced 1/60sec update sweep from the
> serial port on the Video rams; does the output network have the
> capability to accept what is effectively a doubling in output bandwidth
> (especially the RGB D/As)?  If we get a 1/60sec full screen
> update does the Amiga monitor have the bandwidth to accept it?
> 
> All this is just speculation but I am interested in the input of
> those more knowledgeable on electronics, video drivers, and amiga
> software/hardware in adding their two cents as to feasability, implementation,
> and possible alternate approaches.
> 
I have been working with graphics systems for some time, and though the things
you propose are "possible" they may not be desirable.  In the "old days" we
used to get rid of the flicker on high-res (1024x1024) displays in a manner
not too different than you describe (but monochrome).  There are, however,
a few limitations:  1) the monitor (in it's present state) would not have the
ability to go that fast!  You would need a monitor with TWICE the scan rate,
and proportionately higher video bandwidth.  2) the Amiga monitor is
and ANALOG input device, so you would need to have a D-to-A in your circuitry
as well, if you COULD get the monitor to go faster. (I know this is no big deal
as you could use a couple of HC244's and some resistors to sum the signals into
a transistor like the folks at Amiga did). 
If you had a sufficiently high bandwidth monitor around, you could do an
external frame buffer to save the alternating fields at the "each half per
1/60th second" they come out and send them on to a 60 frame per second monitor,
but the cost of the external ram and state machine to make it all work would
end up costing you more than the high persistence monitor, unless you were
really into high volume production.  If you don't already have the high speed
monitor, you'd have to spend far more for the fast unit than a long persistence
one.
(The Amiga monitor, like most alternate field monitors or tv-similar timed
devices, gets it's "doubled" resolution by starting the second field 1/2 of
a line thickness down from the "normal" first line.  Television was the first
commercially produced consumer device to do this,  Any beginning tv service
or tv fundamentals book at your local library can give you the details.  It's
assumption is that the adjacent pixels are not of wide contrast levels like 
we so often see in high-res text applications, etc.)

Don't give up on getting something to work for you, It's the people that 
wouldn't accept what they had that made products like the Amiga a reality.
Keep thinking.....Maybe you'll find something that others have either
overlooked or just had to discard in the fight to make a product as cost
effective as possible.    

-- 
--Rick Frazier--  DISCLAIMER: The above is individual opinion (the result of my
imperfect recall of facts, real or imagined) in no way representing anyone else.
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