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Plans for the next year over ar S100Computers.com

I wrote the e-mail below to a few people, then I realized I should mention it to this complete group since others might be interested and can participate.

Let me outline  the plans for my S-100 system for the next year. Below are the stages:-

8086 CPU board. Prototype done, runs rock solid at 8MH for past two months.  Andrew is finishing up on the final board layout. 

Finished a layout of an 80286 board. Andrew is optimizing layout for a prototype board.  This board is based on a 30 year old S-100 wire wrapped board I have. Again I don’t anticipate any problems. Both boards can be masters or bus slaves (i.e. share the bus with other CPU's).

Unfortunately the 80286 is really brain dead when it comes to MM. It's really just a faster 8086.  Nevertheless it's an important hardware stepping stone for the boards below because the non-multiplexed address/data  lines, BHE,  etc. are the same.

The most immediate CPU goal is an 80386. ( I have in mind others up the food chain but will not get into that now).  While the 80386 does not have the 8, 16, or 32 bit dynamic bus sizing of the 68K family, it does have a pin for bus widths of 16 or 32 bits wide.  This makes it easy to put it on the 16 bit  S-100 bus.  So low RAM could use the S-100 bus. To really use speed/RAM I am going to have a ribbon cable/Bus connector on the top of the board to a second S-100 memory board. This way we should be able to get to the Gigabyte range with DRAMs.   I/O, INTA's  are straightforward.

On the software side I am currently doing a IBM-PC look alike ROM/BIOS.  I have the complete source code for the AT-ROM and am splicing in/out sections of my own very extensive monitor/ROM.  The final idea being that a standard MS-DOS disk should boot and "think" it is talking to a PC.   Generic MS-DOS programs of course will not be a problem but anything that talks to the screen directly (many programs unfortunately) will not work using our Propeller Console-IO VGA board. 

That I why I am looking for the easiest way to have a PC-Video board on the bus.  The Lomas video board:-


 (which I have) did this very well. However it has 4 PALS and is a 4 layered board (with keyboard interface, timer etc).   I have looked around for a simple 6845 video circuit that emulates a VGA. So far nothing other than the slow original convoluted IBM-PC color board.

The best solution would be the later "all in one" VGA emulator chips.  In some case there is just one chip and RAM.  As an added plus they are capable of better resolution that the original PC/6845. The problem is most of these early chips are no longer supplied by Digikey, Jameco, Mouser tec.   As we move to the more recent ones like Nvidia etc things are too complicated.

Way back in the early 80's I did do an S-100 to IBM-PC, S-100 converter board.  I wrote an article is  Sol Libs Microsystems Journal about it.  It connected via a cable to an isolated ISA bus. It allowed you for example to run an IBM-PC color video board directly. With the 6MHz 8086 I had at the time the display speed was decent.   However it had 74121 single shots which had to be tuned depending on the speed of the S-100 bus signals to get things exactly right. Hardly an elegant solution.  That said I may have to in the end go back to this approach using 7474's etc. and a piggy-back PC ISA/video board. However would rather not go that way.

With a 32 bit system and local RAM on board with the CPU,  a real fun computer could be built.   Later we could go to laptop Intel CPU's where the sky is the limit.

I have further hardware and software plans but the above is (hopefully) on the 1 year horizon.