Re: clock unit

On 2013-05-14, at 13:36, Gerrit Heitsch wrote:
> 
> Until we know the actual circuit we can only guess, but with 2 Crystals, the 2 frequencies are not in sync as they are with the old PLL circuit based on the 74LS629. This should result in a slightly unstable picture on the monitor, especially if you use FBAS/CVBS.

I tried composite and it looks good too. In the sense that not much different from the regular 64.

>>> Ok, if you had a 8701 around, you could use that one.
>> 
>> ? I am not sure I understand.
> 
> The 8701 is the little MOS IC (16pin) used in the C64 starting with the 250425 board and also the C128. It has a pin indicating PAL (LOW) or NTSC (HIGH), you add the proper crystal (14.318 or 17.73447 MHz) and it will supply this frequency as TTL signal and also derive the dot clock from it. MOS made it so Commodore would no longer have to buy the 74LS629 from TI, the only one who makes it.
> 
> Using the 8701 it would be simple enough to make a small PCB as a replacement for the clock board for the SX64.

I got what you meant a bit later but you seem to have forgotten that the whole point was the other way around ;-) We don't need replacement for the SX clock unit because (except of the dotclock crystal) it consists of very common elements and is even placed on a doughterboard. What we need a replacement for is the 8701.

> There is also a little circuit to replace the 8701, it uses a 74HC7046 and some extra logic.

Yes, I know. Nicolas pointed me to this piece of Jens's work.

-- 
SD!
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