Re: Unknown holes in the motherboard of the CBM610

Den Mon, 30 Apr 2018 19:59:21 +0200 skrev Gerrit Heitsch
<gerrit@laosinh.s.bawue.de>:
> On 04/30/2018 07:51 PM, Mia Magnusson wrote:
> > 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?
> 
> I don't remember where, but I read somewhere, that you shouldn't
> connect a TTL input directly to +5V.

Interesting!

IIRC all data sheets indicate that anything between 2.4V and 5V is
treated like a correct "1".

Maybe it's different on different TTL families? The B series uses a lot
of S logic.

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