[net.micro.6809] COCO Question

jlw@ariel.UUCP (J.WOOD) (09/18/83)

I have seen an anomoly with my Radio Shack Color Computer, COCO,
with two video games that I have purchased.  It leads me to believe
that there is a not deterministic power-up condition in the
hardware that the software cannot correct.

For both Donkey King and Zaxxon,  great games by the way,
the system will often come up after the game load and execute
with colors reversed.  Donkey King comes up red/blue reversed,
I think, and Zaxxon definately comes up red/green reversed.
The instructions for Donkey King state that if this
condition occurs that the reset button is to be depressed
until the screen comes up red.  Zaxxon has no such instruction,
but if it comes up bad resetting does the trick.

Is there something in the SAM of the video controller which
makes this so?????


			Signed:
				Confused in Cranbury.



					Joseph L. Wood, III
					AT&T Information Systems
					Laboratories, Holmdel
					(201) 834-3759
					ariel!jlw

jlw@ariel.UUCP (J.WOOD) (09/18/83)

I have seen an anomoly with my Radio Shack Color Computer, COCO,
with two video games that I have purchased.  It leads me to believe
that there is a non deterministic power-up condition in the
hardware that the software cannot correct.

For both Donkey King and Zaxxon,  great games by the way,
the system will often come up after the game load and execute
with colors reversed.  Donkey King comes up red/blue reversed,
I think, and Zaxxon definately comes up red/green reversed.
The instructions for Donkey King state that if this
condition occurs that the reset button is to be depressed
until the screen comes up red.  Zaxxon has no such instruction,
but if it comes up bad resetting does the trick.

Is there something in the SAM or the video controller which
makes this so?????


			Signed:
				Confused in Cranbury.



					Joseph L. Wood, III
					AT&T Information Systems
					Laboratories, Holmdel
					(201) 834-3759
					ariel!jlw

PS
	Please excuse the double posting;  I had to
	create net.micro.6809 first.

				J.

dyer@wivax.UUCP (Stephen Dyer) (09/18/83)

The colors used in Zaxxon and Donkey Kong are actually produced in the
monochrome mode, PMODE 4, and I believe are artifacts of the NTSC system.
As you have guessed, software cannot tell which color, red or blue,
is actually produced on the screen.  I do not know what in particular
causes this anomaly (I'd like to know, myself.)

/Steve Dyer
decvax!wivax!dyer

dya@unc-c.UUCP (09/19/83)

References: wivax.18680


     Colour phase difference might be 180 degrees here (or close.) The CoCo
might not insert the "correct" burst with the proper relationship between
lines (there is a specified colour subcarrier phasing w.r.t. so-called
"odd" and "even" lines.
     They don't call it NTSC (Never Twice the Same Colour) for nothing.

urp!unc-c!dya