RE: Commodore joystick ports

From: Scott McDonnell (
Date: 2007-04-11 03:50:30

> -----Original Message-----
> From: 
> [] On Behalf Of john/lori
> Sent: Tuesday, April 10, 2007 2:47 PM
> To:
> Subject: Re: Commodore joystick ports
> Scott McDonnell wrote:
> > At 3mA, the 1nF cap would charge in one clock cycle, at 10uA it
> > would take 256 clock cycles.
> > 
> > (5V would equal 1 and 200mV would equal 255)
> So why don't you have the 1nF cap in your simulation?

Because it wasn't necessary and the refresh rate of the DMMS would 
not be able to track the current visually.

> What's the simulation do when it is there?

The global climate changes and cats begin their take over of Earth! :)

J/K... it charges the cap in a given amount of time based on the current
supplied and as determined by the RC formula.
If I add in the cap, an o'scope, and a switch to discharge the cap, 
you can watch the charge time change depending on the current as given 
by the RC formula. No magic. The DMMs just show nothing useful because 
they are not fast enough.

The charge rate of a cap is predictable given a certain current. So all 
that was required in the simulation was to show the current ranges. The 
rest should be predictable based on established science (to some

The 270 ohms was added since it is in series with the cap and I wanted
to know the exact current that the cap would see. It doesn't make too 
much difference if I remove it.

I was still going on the 2.5V charge threshold. I need to adjust it for 
the 2V that Jim determined through experimentation. It might not make
of a difference, though.

Scott McDonnell

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