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

14 May 1999

On May 15,  0:45, Tony Duell wrote:

...
  To get back to the video ULA, it contains (AFAIK) no
DACs, because the
 Beeb essentially worked with 3 TTL level signals for the video output
 (that were encoded outside the ULA for composite PAL). Said ULA contains
 just about all the video data path logic between the RAM data bus and the
 RGB outputs (in other words the palette, pixel mux/shift register,
 bits/pixel control logic, etc). That's most of the video data path. The
 other part of the display system - the address generation - is provided
 by the 6845. 
Yes, you're right there, of course.  I must remember to engage brain before
putting keyboard in gear ;-)  Especially when short of sleep.  I've worked
on literally hundreds if not thousands of the things, so I should have
remembered a bit better!

...
  I know that darn linear PSU. It had separate 7805s for
the 3 outputs that
 fed the main board.... 
There were no less than three versions of the black linear PSU.  None of
them were satisfactory, but only one, the "adapter and converter", earned
the obvious nickname.

...
  All the docs I've seen imply that any device
connected to the tube or the
 1MHz bus shouldn't draw significant power from the 5V line on those
 ports. Connecting to the 'disk drive power connector' on the PSU can was
 OK, of course. But most (all?) external devices had their own PSUs. 
If you draw too much from one connector, on Issue 3 or earlier PCBs, you
can end up with a significant voltage drop.  It's OK on later ones.

-- 

Pete						Peter Turnbull
						Dept. of Computer Science
						University of York