Z80 home brew with FDC

Roy J. Tellason rtellason at verizon.net
Mon Sep 22 11:56:56 CDT 2008

On Monday 22 September 2008 10:12, dwight elvey wrote:
> Hi
>  Its a shame that the more easily available 555 chips don't
> work well into the Megaherts. They are easy to get and a
> pair of them would have made a reasonable separator.
>  I have a schematic for the separator used on my Polymorphic
> computer. It uses another hard to get VCO chip. It uses
> a MC4024, an external charge pump, 96L02 oneshot and
> a few more TTLs.
> Dwight

I may actually have some of those,  they were used in certain versions of the 
c64 along with the 74LS629...

> > Date: Sun, 21 Sep 2008 23:38:07 -0700
> > From: eric at brouhaha.com
> > To:
> > Subject: Re: Z80 home brew with FDC
> >
> > Allison wrote:
> >> It can also be done with a small amount of ttl.
> >
> > An analog PLL data separator using a 74LS629 VCO or the like is fairly
> > easy to make, though you do have to be somewhat careful with the PCB
> > layout. IIRC, such a design is given in the 179x app note.
> >
> > Building a good digital data separator out of TTL takes a fair number of
> > parts, which is why it was so rarely done. The DPLL design in the 179x
> > app note isn't very good.
> >
> > Eric
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