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Re: RGB Card Question

mdj wrote:

bieling@terra.es wrote:



I just looked at it on a //e, and the burst stays on for all lines
in mixed mode.


Really ?
The 4 bottom lines are text... Isn't it off while in text mode ?
What is driving the color killer circuit then ?
What is gating the burst in ?



I would suspect that the TEXT/GRAPHICS softswitch triggers it.


Correct, and the TEXT softswitch is off in MIXED/GRAPHICS mode.


LOOP:
LDA TEXTMODE
WAIT (A FEW TENTHS OF A FRAME)
LDA GRAPHICSMODE
WAIT (A FEW TENTHS OF A FRAME)
JMP LOOP



It's possible in this case that the killer doesn't activate until a
video cycle ends or starts. I'd suspect that the colour burst being
absent in the middle of a frame would produce pretty bizzarre results.


It is definitely an undefined case for a color monitor.


Someone would need to hook the machine up to a CRO and examine the
video signal to see what's really happening; looking at a display and
guessing isn't a very good test.


That's what I did.  The burst is on for the entire frame.


In either case, it matters not - handling colour/mono on an RGB adapter
is done either by a sequence of mode switching or with a physical
switch. Any new design would probably be best to implement both
schemes.


Right.

-michael

Parallel computing for 8-bit Apple II's!
Home page:  http://members.aol.com/MJMahon/

"The wastebasket is our most important design
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