From: Scott McDonnell (netsamurai_at_comcast.net)
Date: 2007-04-11 15:58:57
Hmm... played with a simulation a bit more on the o'scope and it doesn't work out quite right. john/lori called it with the voltage changing as the cap charges. When I had the scope on there yesterday, I could see varying charge rates, but I hadn't bothered to measure them. Thanks for pointing that out. So, let's get back to the basics here. Here's the raw numbers, compiled here: Cap is 1nF (C64) to 2.2nF (SX-64) CD4066 causes approx. 250 ohms in series with the cap Cap is *grounded* to discharge for 256 cycles. SID counts how long it takes for the cap to charge to threshold voltage (2V) 2V is 40% of VCC (5V) 1 count is 1uS, 256 counts is 256uS Current needed to charge the cap to 40% in 1uS is 2.5mA, equiv. resistance is ~1.9K Current needed to charge the cap to 40% in 256uS is 10uA, equiv. resistance is ~501K This is what needs to be emulated. We have 5V, Ground, and POT lines to work with from the control port. Back to the drawing board. Scott M. Message was sent through the cbm-hackers mailing list
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