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
Received on Sat May 15 1999 - 03:38:04 BST