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
Received on Fri May 14 1999 - 02:27:51 BST