Guys just an update here. I got back and built up the prototype SBC, see here for a picture (ignore text) http://s100computers.com/My%20System%20Pages/SBC%20Z80%20Board/SBC%20Z80%20CPU%20Board.htm Its running at 10MHz with 60K RAM and 4K ROM. I’m using the USB port to control it from my PC. Reworked the MASTER.Z80 monitor so in default mode (IOBYTE = FFH) it uses the USB port for console I/O. One can add the various other S100 boards to the system as you need. For example the Propeller driven Console IO board, speech synthesizer etc. etc. Seems real reliable. Changing the IOBYTE switch settings you can re-direct the output to the Console IO board etc. You all know the drill… Anyway I’ve been rethinking the board layout and realize I can do a much better board with the following extra characteristics. I will remove the onboard Propeller chip, support circuitry, jumpers 3.3V supply etc. and in its place put in the IDE/CF board core circuit. Hopefully with minimal software changes. Again no GAL’s, will be all TTL. Also I have figured out a way to utilize memory banking with that 128K RAM chip so we can also have CPM3 in banked mode. This unfortunately this will require another prototype and push things back a few weeks but it will be a much better board. It alone in the bus with a simple USB connection to you PC would get a system going. Other boards can later be added and parts of this board deactivated, One nice thing about USB -- there are no baud rates, parity stop bits etc. – something that floors most beginners. Update for the hard core users! I have the CPLD based 80386 prototype board up and working (using a 70MHz oscillator) , that’s the good news, The bad news is that our GAL based S100 bus 16MB SRAM board does not behave well at high speeds in the bus. Much to my amazement the earlier 74xx based circuit boards (4MB & 16MB) behave much more reliable. I’m at a loss to explain. But after screwing around now for a few weeks on this project I have decided to do (yet another) 16MB static RAM board. The prototype has gone out. It will utilize our V06c mezzanine boards (unchanged ) of course. I also have redone the power distribution and managed to double the size of the board traces. I need to stress all the above applies to only the new 80386 board. All the past CPU boards work fine with the GAL based RAM boards. The above SBC has sidetracked me in working with the 80486 prototype board. Its sitting here! Hope to get to it next week once I get the V2 SBC layout done. I will be curious to see how that one behaves. Anyway stay tuned John |