[Coco] replacing main rom

[jdaggett at gate.net]

William

The Coco 3 was the first of the Cocos to have attributes for the text 
characters. Bit 7 of the attribute byte controls character blink at a 
half second interval. Clearing and setting that bit controls the 
character blink attribute as long as the COCO bit of INIT0 is 
cleared. If set then the attributes are not functional. 

The cursor blink is done in the basic rom as far as I can tell. Looking 
through the unravelled series I have yet to see where the IEN and 
FEN bits of INIT0 are set. That means in normal startup the Coco3 
is useing the IRQs from the PIA chips. 

It is my contention that the character blink attribute is either used by 
other programs. I also do not believe that the timer is used, instead 
there is another internal timer that is used to determine character 
blink interval. This timer has as its input the vertical rate of 59.94 
Hz. Count to 30 and you have about one half second. So the 
character attiribute is flipped every 30 vertical frames. 


james


On 11 May 2005 at 16:01, William Astle wrote:

Date sent:      	Wed, 11 May 2005 16:01:03 -0600
From:           	William Astle <lost at l-w.ca>
To:             	CoCoList for Color Computer Enthusiasts 
<coco at maltedmedia.com>
Subject:        	Re: [Coco] replacing main rom
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> jdaggett at gate.net wrote:
> > Art
> > 
> > My search through the code has yielded no such usage of the timer by
> > the Super Extended Code at all. I also do not see where there is any
> > patch in the blink routines to allow for the GIME timer to control
> > the blink time. 
> > 
> > I maybe wrong and have not found any reference to the GIME timer
> > usage though.
> > 
> > This does seem to support the basic belief that the GIME timer was
> > for program development for games or other means.
> 
> Super extended basic initializes the timer to the maximum possible
> value (IIRC) in one of the "block transfer" initialization bits. There
> is no software setting to enable or disable the use of the timer to
> control the blink rate - the GIME just uses it to do so. If the timer
> is disabled, text doesn't blink.
> 
> > 
> > james
> > 
> > 
> > 
> > On 11 May 2005 at 15:33, Arthur Flexser wrote:
> > 
> > Date sent:      	Wed, 11 May 2005 15:33:47 -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>
> > 
> >>On Tue, 10 May 2005 jdaggett at gate.net wrote:
> >>
> >>
> >>>To my knowledge I am not sure that the Coco 3 rom uses the timer
> >>>for anything.
> >>
> >>I seem to recall that the timer is used by Super Extended Basic for
> >>controlling the cursor blink rate on the 40/80 column screen.
> >>
> >>Art
> >>
> >>
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> > 
> > 
> > 
> 
> 
> -- 
> William Astle
> finger lost at l-w.net for further information
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