Hi
Here is a little background on the S100computers & N8VEM S-100 board development from my perspective. Hopefully John can chime in on his thoughts as well.
The S-100 to ISA bridge board (aka S-100 TestIO V2) is really a development tool we've created to help get the S-100 VGA board working -- similar to the ISA VGA board we designed a while back. The VGA chipset has a problem with the S-100 bus we haven't been able to find yet. The same chipset works on the ISA bus just fine so this is an intermediate step to get our working ISA VGA board onto the S-100 bus and narrow down the problem area. Eventually this is going to result in a native S-100 VGA board.
However, the S-100 to ISA bridge may be quite a useful tool in its own right. I certainly hope so but its a side effect not a main goal. It probably needs some additional work to make it more general purpose but is definitely showing major progress. It is based on John's initial 8 bit ISA to S-100 design which I originally was advocating as a useful board. However I now see John's point on the more broader application of the 8 <-> 16 bit ISA conversion logic. I am hopeful this new board is going to bring us closer to a general purpose S-100 to ISA bridge board.
The S-100 VGA is such an important project to accomplish that we are pulling out all the stops to get it working. There have been multiple false leads, dead-ends, and non-working prototypes. However so much of the current Linux/BSD development basically assumes a VGA that without it there will be major compatibility problems. Our major development centers on basically three boards: S-100 80386 CPU, S-100 80386 SRAM, and S-100 VGA. It is also the basis of modern x86 PCs since about 1985 (386 + RAM + VGA). Everything afterward stems from it.
The S-100 ParallelIO board is a kind of a re-imagined version of the IMSAI PIO board. Basically a simple board that's useful for everyone but still easy to build and get working. It adds LEDs for debugging purposes and a general purpose PC compatible parallel printer port. With 4 input parallel ports and 4 output parallel ports and various other control signals there is a lot you can do with this board and I think it is going to be a hit. After several complex boards it is a nice change to work on something relatively straight forward.
The S-100 VDP is kind of an S-100 off-shoot of the video and sound section of the N8VEM N8 board and/or SCG. By itself it provides video (composite and sort-of-VGA) and a sound generator. It is a fun board and could be potentially useful for many things on an S-100 system. I am hoping it can be used to bring some level of MSX hardware compatibility to the S-100 bus but it is not restricted to only a Z80 CPU or the unique MSX memory bank switching scheme.
The S-100 VDP is part of another trio of boards designed to eventually allow full MSX hardware compatibility on the S-100 bus. First is the S-100 Z80 CPU board which already exists, second is the S-100 VDP which implements the video and sound sections, and finally is the S-100 Utility board which fills out the MSX hardware compatible memory "slots" and the basic IO (parallel, serial, matrix ASCII keyboard, & cassette control functions). The S-100 Utility board can also be used (like the S-100 VDP) separately from MSX as a basic 8 bit S-100 ROM, RAM plus IO board. The alternate goal being this board could be used to "bootstrap" a minimal S-100 system using a CPU board plus the S-100 Utility board only.
Many things happening on the S-100 bus these days. Feel free to join us!
Thanks and have a nice day!
Andrew Lynch