Acorn RiscPC 600 (OT - only 5 years old) - test-drb@ccmp.vtda.org

13 May 1999

On May 14,  2:36, Tony Duell wrote:
...
  Pete wrote:
 > The Beeb video architecture is very similar to the Atom (but more modes,
...
  > more colours, more resolution), the disk system
is almost identical, the
...

 Not really. The Atom is based on a 6847 (and uses the address generator,
 display data path, character generator, etc of that chip). There is some
 memory associated with the display system only.

 The Beeb uses a 6845 to generate display addresses in main memory. The
 video path is mostly in a custom chip ('Video ULA'), with the character
 generator (only used in the Teletext mode, Mode 7) in an SAA5050 chip.

 I would not call those 'similar'... 
Don't confuse the implementation with the architecture.  Sure, the Beeb
uses an SAA5050 for one (of eight) modes - but the others work in a way
very similar to the Atom.  Actually, very little of the video path is in
the ULA on a Beeb.  It contains the DACs and the palette only.

...
  > The Arc (not Arch, please :-)) was certainly
built from the same philosophy
...

 The 'h' is silent, but most references to that machine call it the Arch...

Not those I've seen.  All the Acorn people I know (and I know lots, don't
forget I worked in that world for ten years) use "Arc".

...
  The fact that the processor runs at twice the speed
(2MHz) in the Beeb
 helps as well :-) 
Agreed.  But it's about 4 times the speed of an Apple ][, which runs at
1MHz.

...
   properly
buffered and streamed.  What's wrong with the 1MHz bus for
 expansion?  There were lots of devices that used that, including a 
 Nothing at all. It's just that the Apple was easier to make cards for
 than the Beeb (where you have to provide an external PSU and case (you
 shouldn't attempt to power external devices from the BBC PSU). 
The switch mode PSU (not the linear "adapter and exploder" used on the
first batch) has quite a lot of spare capacity (about 2A at 5V), and an
external output connector.  It was *designed* to power external devices
(mainly disk drives, but it is perfectly capable of powering other things
too).  And there are power connectons on some of the device I/O connectors
including the Tube and User Port.

...
  I was under the impression that the Acorn host adapter
didn't support
 multiple masters, and was thus better classed as a SASI host... 
Many early SCSI systems didn't.  It does, however, support CCS.

...
  > think Torch's was SASI -- and it never worked
very well, I seem to recall.
...

 Torch did 2 versions. The common one was SASI, and wasn't that good.
 There's also a much rarer SCSI unit (the ROM for it is called SCSIfs). It
 works pretty well. 
I didn't know about the later one, I admit.

...
  > MOS.  They were issued at Acorn training courses,
which were run for
 > dealers and developers.  There were a range of courses, and I went to one
...
   of the MOS
courses run by Paul Bond (who was the major designer of the
 MOS).  It was a fascinating course. 
 OK, it wasa never available to %random-user.... Or to be more specific, I
 couldn't get it :-) 
They did cost money (though not an awful lot), so yes, they wouldn't
attract the average enthusiast, but a lot of them were attended by teachers
and school technicians.

...
  Well, the original 'proton' never existed as a
production machine AFAIK. 
Yes, only as development prototypes, as far as I know.  I never saw one,
only pictures (and I'm not sure they weren't mockups).

...
  But the name was certainly used - and used in Acorn
documentation - as a
 code name for the BBC micro. For example the diagram 103,008 is called
 'Circuit Diagram for the Proton Final Test Jig', and is the final test
 jig for the BBC micro (or at least a machine with identical 1MHz bus,
 printer port, user port, analogue port and cassette port). 
Yes, but Acorn staff had a habit of reusing names on diagrams that were
redrawn.  It doesn't mean that that board was actually a Proton board by
then, although it must at least have started life as one.

...
  In fact the
 103 identifies it as being a BBC-micro related product (The BBC micro
 schematic is 103,000). 102 series schematics are for the Atom, 100 series
 for the Systems (101 is for what?) 
I dunno -- 104 is teletext adapter, 108 6502 2nd processor, 109 is the Z80,
115 is Prestel, I think.  107 is the 1MHz bus backplane.  101 might be one
of the Econet products, I suppose, or the original proton number series, or
an OEM device.

-- 

Pete						Peter Turnbull
						Dept. of Computer Science
						University of York