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RE: [N8VEM-S100:1834] Re: status of S-100 uPD7220 board

Hi!  Thanks Dave!  It never hurts to have another video board!  Most likely we’ll standardize on the S-100 VGA board once it is done but that may be a while.  The S-100 uPD7220 GDC board will be able to use standard VGA monitors (CRT and LCD) since it uses regular dot-clocks.  The S-100 VDP has VGA compatible signals but still retains the NTSC dot-clock which makes monitor compatibility kind of tricky.  Really the only good options for the S-100 VDP VGA output are really old NEC multi-sync CRT monitors or the newer LCD monitors which share common circuitry with a TV counterpart model.


The NEC uPD7220 GDC is an interesting historical chip in its own right.  I consider it part of those many alternative history discussions like what if IBM has chosen CP/M 86 instead of MS-DOS, used a 68K instead of 8088, used VME instead of ISA, etc.  The NEC uPD7220 was generations ahead of the MC6845 (essentially a glorified address generator) and we’ve been straddled with the latter for thirty years.  It took another 10-15 or so years for accelerated graphics primitives to enter in to the mainstream of PC architecture due to the backwards nature of the MC6845.  What a kludge!


Unfortunately the uPD7220 lacks a BITBLT function however I am sure that had it become popular that function would have appeared soon.  Pair the uPD7220 with a DMA chip and you get the same effect.  Basically just slinging huge hunks of bits around memory address space at break-neck speed.


At least in theory, it would be possible to write an X-server for the uPD7220 but I imagine the performance would be terrible.  For that matter, it would also work for the upcoming S-100 VDP but would have similar results.  Still it is good to have options.


The S-100 uPD7220 as envisioned is an IO only device.  It doesn’t have to be like that but it is how it was implemented on the N8VEM ECB system so I just ported it.  I could alternatively be a memory board (shared between the uPD7220 and system memory) as well but would require a significant redesign.


Thanks and have a nice day!

Andrew Lynch


From: n8vem...@googlegroups.com [mailto:n8vem...@googlegroups.com] On Behalf Of yoda
Sent: Monday, August 19, 2013 5:11 PM
To: n8vem...@googlegroups.com
Subject: [N8VEM-S100:1834] Re: status of S-100 uPD7220 board


Hi Andrew!


Count me in - I think I have all the parts laying around for this.



On Monday, August 19, 2013 3:36:56 PM UTC-5, lynchaj wrote:



I remembered there is another S-100 board that is basically complete – the S-100 uPD7220 GDC board. 


It is in the wait queue like the S-100 6502 CPU V2 board.  All that is needed is some prototype PCBs for build and test.


It is a video board capable of VGA compatible output (640x480 and 800x600) 16 color display with accelerated graphics primitives.


Basically this was the direction of microcomputer graphics prior to the advent of the IBM PC and the rise of the CGA/MDA architecture.




Is anyone interested in doing some build and test on this board?


There is a great source of design information and software here on the N8VEM ECB uPD7220 GDC board




I’d like to raise $150 for some prototype boards.  Anyone interested?  This is a neat board and could be very useful.


Thanks and have a nice day!

Andrew Lynch

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