Date   : Sat, 08 Mar 2008 13:52:20 +0100 (GMT)
From   : johan@... (Johan Heuseveldt)
Subject: TUBE chip, accessing 'Parasite' side

Hi Jonathan,

On Fri 07 Mar, Johan Heuseveldt wrote:
> On Thu 06 Mar, Jonathan Graham Harston wrote:
> > > Message-ID: <Marcel-1.53-0304124938-0b0xSBG@...>
> > Johan Heuseveldt wrote:

[snip]

> > > Therefor, having seen this precaution for VCC, I was a bit disappointed
> > > to see some contention-logic for accessing the TUBE chip simultanously

> > 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.
> 
> If you are really sure about that, then my design - not having similar
> circuitry as in the 6502 2ndP, can be considered as finished. But that
> means Acorn has put a lot of extra chips for the clock and slow down or
> stretching circuits. I find that hard to believe, although I like to be
> proven otherwise! :-))
> 
> The hardware certaily suggests different.

IC27, both FFs for a start!


Hm, I was wondering; I seem to remember a message just a few days ago
mentioning replacement (second generation) TUBE chips, but giving some
problems...
Ah, found it:

[In context of an external CoPro box]

On Wed 05 Mar, Pete Turnbull wrote:
> On 05/03/2008 14:39, Jules Richardson wrote:
> > when Johan wrote:

> > > There is a(n external) CoPro case - by CC I think, specificly designed
> > > to do exactly that!
> > 
> > I had a Watford one (I think it went to Dave Moore), but I think that was
> > more  about the ability to run the Master-series internal boards
> > (primarily the  80186) on a lowly model B.
> 
> There was an Acorn one as well, though never made or sold in any 
> numbers.  It was indeed intended to allow Master-series internal boards 
> to be sold for Beebs, at a time when Acorn (who had unbelievably long 
> lead times) had run out of second processors and didn't want to commit 
> to a large manufacturing run.  It came out at about the same time as 
> Acorn were using two different replacements for the Tube ULA, and I 
> remeber there was some problem over that because one of the replacements 
> worked with second processors but not co-processors (or maybe t'other 
> way round).

So I'm wondering if there are different /types/ of TUBE chips. I think the
6502 Second Processors were one of the earliest Second Processors
available, perhaps using a TUBE chip not having the contention logic inside.
The board electronics can cope with such a TUBE chip, as contention logic is
present /on/ board!

When newer TUBE chips were available which has internal contention logic,
this can be used on boards still having the external contention logic present
and active. As long as the new TUBE chip can handle these
external clock adjustments (slow down or stretching), it should all be OK.

The TUBE chip in my 6502 Second Processor is:

  Ferranti
  ULA9C018E-7
  8416

and is the original when bought this 2ndP new!

So by the time I bought this 2ndP, the boards are the same - still having the
external contention logic - but the TUBE chip was of a next generation?
Could be I suppose?
(board details are: 208.000 ISS4)

So Jonathan, is this a (newer?) TUBE chip; the one that has internal
contention logic for sure, nothing necessary external at all?

Probably it's a good idea to compare with the (65C102) CoPro board. It has
less components I seem to remember, but also a different TUBE chip I think.
I mean, different from the texts on it.

If indeed the TUBE chip is /with/ internal contention logic, then this would
be a big benefit to me, and a huge time saver!


Waiting (for to be SYNChronized),
Johan

-- 
Johan Heuseveldt <johan@...              >
  aka  waarland

  The best place is a Riscy place
 
The light of a hundred stars does
not equal the light of the moon.