Richard Cini wrote:
>
>
> The 9958 is a weird DIP packaging so maybe the 9918. The Retrobrew Computers N8 Home Computer uses it. Looks like the VDP, RAM, three buffer chips and some decoding.

Thanks Rich,

Designing video was "hard" back in the 70s/80s, so there were lots of
specialized controller chips for people eager to get something out the
door quickly. The Motorola 6845 was popular, but each IC manufacturer
had their own. Intel had the 8275/76, RCA had the 1861, TI had the 9958
and 9918, etc.

They all work, but have also become rare and expensive today. I hesitate
to design something with one, unless I have a bucket of them.

So, I'm inclined to follow in the footsteps of Woz, Sinclair, Lancaster,
and other designers who used clever circuits to produce video with
standard chips. I've attached two of my "brainstorms" in this path:

Z80-VID.PDF has 12 ICs, outputs 384x192 pixel NTSC/PAL video (enough for
24 lines of 64 characters), 128K RAM, PS2 keyboard interface, SPI, and a
bit-banger serial port. It's an accessory board for the Z80MC, (kind of
equuivalent to the Z80-SIO), and multiplexes the RAM between Z80 and
video, so the Z80 does not stop while video is being output.

Z80-VIP.PDF has 11 ICs, outputs the same video, but is a complete
free-standing "terminal". It has its own Z80, 32K RAM, 32K EPROM, UART
serial port, and switch matrix keyboard. It uses the Z80's BUSRQ/BUSAK
signals to stop the Z80 while video is being output (so the Z80 runs at
about 25% speed). It's patterned after my 1802 VIP2K
<>, and uses a simple state machine
(counter/EPROM/latch) to create the video.

But both lack "elegance", and have too many parts to fit on an Altoids
card. I could obviously use a bigger board; but keep "scheming" in case
there's a way...

Lee Hart

--
A designer knows he has achieved perfection not when there is
nothing left to add, but when there is nothing left to take away.
???????? -- Antoine de Saint Exupery
--
Lee Hart, 814 8th Ave N, Sartell MN 56377,