From: J Ellsworth (c1_at_syndicomm.com)
Date: 2007-04-09 08:40:21
The dtv had the 512 cycle charge dump type ADC, but for some reason it didn't seem to work well when the chip came back. I was having a conflict with DC Studios, so I didn't spend any time trying to figure out why it was not stable. Jeri -----Original Message----- From: firstname.lastname@example.org [mailto:email@example.com] On Behalf Of Jim Brain Sent: Sunday, April 08, 2007 7:21 PM To: firstname.lastname@example.org Subject: Re: Commodore joystick ports Scott McDonnell wrote: > I agree with you about the 512 cycles, now that I read up a bit more. > > Sorry, there was some miscommunication there about the multiplexing. > There are two POT inputs to the SID and two pots on each control port. > POTX and POTY of the given control port are connected to the SID at the > same time. The PORTS are multiplexed, not the POT lines. This is done by > the CD4066. My mistake in not being clear. > It wasn;t your post I was referring. Someone (Pasi?) suggested the 512 might be to allow the internal circuitry to be multiplexed, 256 for POTY, 256 for POTX. However, if that were true, I reasoned you should see the drive to zero trigger alternate, and it does not. > I am fairly certain Jeri just used a modern ADC, since it wouldn't make > much sense to do it exactly the way the original commodore worked when > there are better and easier ways now. There is an ADC chip connected to > the POT on the Hummer. I don't have one in front of me, but it is > probably one of the Dallas Semi integrating slope ADCs (dual slope, most > likely.) It isn't important to emulate it exactly, as long as the SID > registers are filled with the values expected by a game. You have a lot > more license to do it your way when you recreate the internals. That's > the secret of emulation: As long as the circuit takes the inputs > expected and outputs the results as expected, what happens in between > isn't all that important. > Given the low sample rates involved and the target (paddle input), your position is correct. However, Jeri is known for trying to deal with the minutiae. As well, using a regular ADC would no doubt preclude the use of the 1351 mouse, which depends on the 512 cycle period. > Again, yours and Levente's methods both work as you both have > demonstrated. Nobody is questioning that, of course. But, I am just > I'm not defending it per se. I had a hammer (uC) for other reasons in my project, so I manufactured the "nail" to make it all work. It's OK, though. Someone asked me to delve into more details on how the PSXJoy emulates the paddles, and I admit I had forgotten a lot of this since late 2004, so it was a good refresher. Jim -- Jim Brain, Brain Innovations (X) email@example.com Dabbling in WWW, Embedded Systems, Old CBM computers, and Good Times! Home: http://www.jbrain.com Message was sent through the cbm-hackers mailing list Message was sent through the cbm-hackers mailing list
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