Date   : Sun, 09 Mar 2008 00:50:17 +0000
From   : jgh@... (Jonathan Graham Harston)
Subject: TUBE chip, accessing 'Parasite' side

Johan Heuseveldt wrote:
> > On Thu 06 Mar, Jonathan Graham Harston wrote:
> > > The contention logic is inside the Tube ULA itself. Each side can
> > > be read and written independantly of what is happening on the
> > > other side.
 
I think we may be talking about two different things. By
contention logic I thought you meant systems that prevented
problems if both CPUs tried to access the Tube ULA at the same
time. That is dealt with by the fact that effectively the Tube ULA
is two seperate devices, on two seperate CPU buses. The parasite
accessing the parasite side of the Tube ULA doesn't interfer with
the host side accessing the host side of the Tube ULA and vic
versa.
 
Just like there's not contention between a computer and a printer
when the computer accesses its parallel port and the printer
accesses the other side of the same parallel port.
 
Now that I think I know what you're talking about, though, I see
that the 6502 and Z80 copros feed PCS and HCS into an OR that
feeds the timing circuitry - probably your cycle stretching.
Interestingly, the 32016 and 80186 copros don't.
 
-- 
J.G.Harston - jgh@...                - mdfs.net/User/JGH
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