[Coco] replacing main rom

[jdaggett at gate.net]

Art

One other point of my thinking. I learned TVs long before 
computers. I at times associate phosphor persistance with scan 
frequencies as they are interrelated. I interchange the two so often 
that I confuse others as well as myself at times. 

I am used to describing what is on the screen as a means of an 
electrron beam striking a set of phosphors that displays what is 
seen. The problem with to fast a blink rate is such that the computer 
blinks a character faster than the electron beam can get back to that 
spot on the CRT to show what the computer has done. Even though 
the computer blinks a character at a certain rate, the viewer sees it 
at a slower rate due to the scan rate is too slow for the computer 
blink rate. 

james

On 13 May 2005 at 19:01, Arthur Flexser wrote:

Date sent:      	Fri, 13 May 2005 19:01:49 -0400 (EDT)
From:           	Arthur Flexser <flexser at fiu.edu>
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<coco at maltedmedia.com>
Subject:        	Re: [Coco] replacing main rom
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> Now that I think about it further, I see more clearly what you are
> saying, though I still disagree with some aspects of your analysis. 
> Since the blink durations for the "on" and "off" periods are
> presumably equal, there will be a 50/50 chance for the blink to be in
> the on state when the relevant range of scan lines for a certain
> character is reached in each frame.  (Sometimes the blink will be in
> the on state for only part of the character, resulting in a portion of
> the upper or lower part of the character not being drawn.)  The
> horizontal scan time is around a 16th of a msec per line, vs. an on
> period, at the fast rate, of about one msec, so whether the character
> is drawn as on or off at the fast rate will depend on which 16-line
> strip of screen it happens to fall into in each frame.  That is, at
> the fast rate, characters with the blink attribute are drawn as on in
> one 16-line strip, off in the 16-line strip just below, etc.,
> alternating over the height of the screen.  Since I believe that the
> GIME timer is not synched with the vertical scan, whether a particular
> character will be on or off in a given frame will effectively be
> random, with 50% probability.  On average, the character will be in
> the on state in half the frames, so its physical blink rate will
> average out to one "on" per two 60th of a second frames, or a 30th of
> a sec (33 msec).  This is true regardless of phosphor persistence. 
> The effect of persistence will be to lessen the difference in
> character luminance between frames where the character is present and
> those where it is absent, reducing the amplitude of the flicker, but
> the flicker rate will still appear as a 30th of a second, on average,
> though the flickering will be irregular.  Which pretty much
> corresponds to what I remember observing when I tried kicking the rate
> up to high.
> 
> Art
> 
> On Fri, 13 May 2005 jdaggett at gate.net wrote:
> 
> > Art
> > 
> > we are talking about the same thing from different perspective. 
> > 
> > What I am saying is that the "apparant" blink rate and not the
> > actual blink rate. Due to the persistance, only about every 10th
> > blink is seen on the screen. The phosphur cannot change fast enough
> > to see the change in every field of the raster scan. 
> > 
> > james
> > 
> > 
> > On 13 May 2005 at 14:09, Arthur Flexser wrote:
> > 
> > Date sent:      	Fri, 13 May 2005 14:09:17 -0400 (EDT)
> > From:           	Arthur Flexser <flexser at fiu.edu>
> > To:             	CoCoList for Color Computer Enthusiasts 
> > <coco at maltedmedia.com>
> > Subject:        	Re: [Coco] replacing main rom
> > Send reply to:  	CoCoList for Color Computer Enthusiasts 
> > <coco at maltedmedia.com>
> > 	<mailto:coco-
> > request at maltedmedia.com?subject=unsubscribe>
> > 	<mailto:coco-
> > request at maltedmedia.com?subject=subscribe>
> > 
> > > I disagree.  Putting it in other terms, the persistence should
> > > decrease the amplitude of the variation in luminance, without
> > > affecting its frequency.
> > > 
> > > Art
> > > 
> > 
> > 
> > 
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