On Tue, May 29, 2018 at 5:03 PM, Gerrit Heitsch <gerrit@laosinh.s.bawue.de> wrote: > On 05/28/2018 09:24 PM, Francesco Messineo wrote: >> >> On Mon, May 28, 2018 at 8:51 PM, <silverdr@wfmh.org.pl> wrote: >>> >>> >>>> On 2018-05-28, at 14:28, groepaz@gmx.net wrote: >>>> >>> >>> >>> Interesting. Due to VCO? And the original clock circuit with discrete >>> elements? There was AFAIR also a kind of PLL involved. Do those exhibit the >>> same problem? >> >> >> the original C64 clock generator circuit (is) a regular PLL (so, not >> "a kind"), the reference divider circuit is inside the VIC-II IC which >> is part of the PLL. > > > But the design of the PLL on the old C64 is a bit on the dirty side when you > look at the part of the circuit containing the 74LS193. hm? It's a typical design of the era, I've seen several PLLs where a divider is made with a counter pre-loaded to a specific value and counting either up or down with one bit being the output. I find also clever using a half LS74 as a NOT port, since it was free anyway. What do you consider dirty? It's almost impossible to use less ICs for that design, I'd say it's clever and cheap for that era. When I was making my own 8701 replacement, one of the designs I ended up with, used the same amount of ICs as the original Commodore PLL, but I had to use an additional divider since the 8:1 divider from VIC-II isn't accessible from the 8701 socket. In the end I've found a single chip (plus bypass, plus some resistors) circuit that could do the job, but that wasn't available in the '80s. F >Received on 2018-05-29 18:01:31
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