On 10/11/2016 06:10 PM, Jim Brain wrote: > > The SID POT ADC circuitry needs to drag the line hard to ground for 256 > cycles. NMOS would easily handle this, but it must be a pretty hefty > transistor to ensure it can overcome the current coming from the paddle > resistor. I don't see such a transistor on the 6581 die shots, but it > must be there. What should I look for? When looking at http://mail.lipsia.de/~enigma/mos6581r4/full_q30.jpg the paddle inputs should be the 2nd and 3rd pad from the bottom on the left side of the die. Between them is a mirrored structure which should be the measuring circuit. Close to each pad, I can see something that looks like a transistor that connects the pad to the GND line. But it's a lot smaller than the drivers for the data pins. The paddle resistors are 500K max, but I don't know what their minimum value is. The schematics suggest that it's zero, but that would be more than any NMOS driver can handle... Gerrit Message was sent through the cbm-hackers mailing listReceived on 2016-10-11 18:00:24
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