Re: [stella] 2600 questions

Subject: Re: [stella] 2600 questions
From: Mark De Smet <de-smet@xxxxxxxxxxxxxxx>
Date: Wed, 21 Jun 2000 17:55:32 -0500 (CDT)
> >Yes, paddle reads must be done during the screen.
> How many scanlines can you spread out the reads in order to still achieve 
> accurate results?

Someone with experience with paddles?

> >may want to catch.  With the latch, you can catch all presses, no matter
> >how fast(I lie, the speed is limited to the transistor speed, but that is
> >pretty darn fast).
> With the latching, most 2600 games won't allow autofire over 30 times a 
> second then, right?  One on and one off state on alternating frames?

The latch simply locks the data until you clear(set) it.  Once
cleared(set), the latch is going again.  If you simply clear(set) it, and
read it again next frame and see that it is set(clear) again, you can't
tell if the button was released and pressed, or if it was continuously
pressed.  If you want to only read once per frame, and must determine the
number of presses, then yes, the theoretical max number of presses is
30/sec.  However, if you read it, clear(set) it, then immediately read it
again, you can use the second read to check if the button is currently
released.  This way you can theoretically count up to 60/sec.  The only
flaw to these numbers is an interferance pattern you may see if the
presses are 29/59 per sec, but that is another story.

> What happens when you hold down the fire button close to the end of a frame 
> and in the middle of the next frame you release it and then manage to press 
> it down again by the end of the frame?  What state will the register be in 
> when it's read in vertical blank?

Assuming that you are reading the register in vertical blank/overscan etc,
then you won't be able to tell the difference between that scenario and
holding the button.  This is effect the interferance case can cause.  If
you want to do edge detection, you can use the interrupt logic in the
PIA(only for the joystick or paddle buttons).


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