Message-ID: <445@sdcsvax.UUCP>
Date: Sat, 3-Nov-84 21:07:18 EST
Article-I.D.: sdcsvax.445
Posted: Sat Nov  3 21:07:18 1984
Date-Received: Tue, 6-Nov-84 04:11:12 EST
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Organization: EECS Dept. U.C. San Diego
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Here's a stomper for ya.

How is the clock and the user port 1 related? 

It looks as if user port one can somehow ground out the clock or slow
it down. For the 100,000 dollar question --> WHY?

If any one has noticed that when the joystick is plugged in the user port 1
and is pulled all the way to the left the clock cycles seem to be slowed
down by a factor of almost 10? If any one has noticed this idiosync. of
the C64 please post why. I will try and solve the little problem -

rich
UCSD

Message-ID: <16800015@uiucdcsb.UUCP>
Date: Mon, 5-Nov-84 12:33:00 EST
Article-I.D.: uiucdcsb.16800015
Posted: Mon Nov  5 12:33:00 1984
Date-Received: Wed, 7-Nov-84 06:37:07 EST
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Nf-ID: #R:sdcsvax:-44500:uiucdcsb:16800015:000:502
Nf-From: uiucdcsb!miller    Nov  5 11:33:00 1984

Most of these questions have been discussed before by us "old timers".  I
realize, however, that new people are always joining the group.  What you
described with port 1/west/fire button not pressed is that the c64 uses the
same hardware to read its keyboard.  Hence, some joystick configurations get
mapped into chars.  That particular situation maps to the Control key, which,
as everyone knows, slows the screen scrolling down if the cursor is at the end
of the screen.

A. Ray Miller
Univ Illinois

Message-ID: <2463@ihuxf.UUCP>
Date: Tue, 6-Nov-84 08:23:10 EST
Article-I.D.: ihuxf.2463
Posted: Tue Nov  6 08:23:10 1984
Date-Received: Wed, 7-Nov-84 08:12:03 EST
References: <445@sdcsvax.UUCP>
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Organization: AT&T Bell Labs, Naperville, IL
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It slows things down because the joystick ports are polled
by the same hardware as the keyboard is.  Some of the joystick
positions map to keys.  The effect of pulling the joystick
in port one all the way to the left is the same as holding
down the CTRL key during a listing.  As far as I remember
they are electricly identical.


Happy Hunting

			Mike Nelson
			AT&T Bell Labs
			ihuxf!cuda

Message-ID: <194@terak.UUCP>
Date: Mon, 12-Nov-84 15:18:21 EST
Article-I.D.: terak.194
Posted: Mon Nov 12 15:18:21 1984
Date-Received: Sat, 17-Nov-84 04:33:55 EST
References: <445@sdcsvax.UUCP>
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Organization: Terak Corporation, Scottsdale, AZ, USA
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> If any one has noticed that when the joystick is plugged in the user port 1
> and is pulled all the way to the left the clock cycles seem to be slowed
> down by a factor of almost 10? If any one has noticed this idiosync. of
> the C64 please post why. I will try and solve the little problem -
> 
> rich
> UCSD

Shooting from the hip...

No, I never noticed, but I'll speculate about the cause anyway.
Moving the joystick to the left is the same as pressing the
CTRL key on the keyboard.  The keyboard is scanned at 1/60
second intervals by using the 6526 timer interrupt.  The clock
is kept by counting 60 such interrupts as one second, etc.
A feature of the 64 is that holding the CTRL key down will
slow down screen scrolling enough that you can read it.

Now, for the Olympic event, conclusion broad-jumping.
The slow-scroll feature is probably provided by a delay loop
in the timer interrupt routine whenever the CTRL key is held
down.  This makes for a significant delay before requesting
the next interrupt, 1/60 second later, so that the 6526
timer interrupts are much less regular than 1/60 second.

Good luck chasing it down!

   Doug Pardee -- Terak Corp. -- ...!hao!noao!terak!doug