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, www.sunrise-ev.com
Lee Hart