Re: Unknown holes in the motherboard of the CBM610

Den Mon, 30 Apr 2018 19:08:59 +0200 skrev Francesco Messineo
<francesco.messineo@gmail.com>:
> On Mon, Apr 30, 2018 at 7:05 PM, Mia Magnusson <mia@plea.se> wrote:
> > Den Mon, 30 Apr 2018 15:00:41 +0200 skrev Michał Pleban
> > <lists@michau.name>:
> >> Hello!
> >>
> >> Mia Magnusson wrote:
> >>
> >> > My intention is to find some kind of suitable software for timing
> >> > diagrams (I was first thinking about project management software,
> >> > but there seems to be software especially made for thins
> >> > purpose).
> >>
> >> Why not simply attaching a logic analyzer to various signals and
> >> measure what the real hardware does?
> >
> > Everything is made of standard 74xx circuits and standard DRAM's
> > (except the CPU and the CRTC) and it would be really nice to know
> > that the maximum and minimum delays is for each part of the
> > circuit. (The 6525's doesen't count in this discussion as their
> > timing isn't critical to understanding how the complicated
> > CPU-RAM-Refresh-Coprocessor stuff works).
> >
> > I wounder if anyone who designed or in general worked with the
> > hardware on theese machines at Commodore are still alive and
> > remembers some stuff? For example it would be nice to know why some
> > signals are called PUP1 and PUP2.
> 
> look if they're static pulled up to some resistor to Vcc... PullUP1,
> PullUP2... Just guessing, but I use a similar naming scheme when I
> design my own boards.

Thanks! Yes, they seem to go to pull-up resistors.

But why not just join each of those TTL inputs with +5V directly on the
nearby chip?

Does some 74xx IC's work better with slightly less drive to +5V on the
signal that feeds the inputs?

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