From: n8vem...@googlegroups.com [mailto:n8vem...@googlegroups.com]
On Behalf Of Fabio Battaglia
Sent: Monday, March 17, 2014 4:03 PM
Subject: [N8VEM-S100:2769] Status of my S-100 system (With nice low-res pictures!)
Finally, after a few months of part-sourcing and board-buying (Thanks to Jack Rubin and Matthew Turner for their spare boards) I have some initial output from the S-100 system I'm building!
I started my build with the V1 of 6502 CPU board and the Propeller driven Console IO (not counting the bus terminator and extender cards).
Why did I choose the 6502 board instead of the more useful and common Z80 board? Mainly for two reason: lower IC count and simpler circuits. Being totally new to S-100 system I found myself in a chicken-egg situation: I needed some working CPU card to output
data to show on the Console card, and a Console card to see the output of the CPU board.
I thought the 6502 card to be a good choice because of a lower number of ICs that I needed to debug (and indeed I ended up with a damaged 541 which I had to replace before getting the card to work...) and I choose the Propeller driven Console card instead of
a serial board because most of the complexity was contained in the propeller chip.
The hardware "bootstrapping" ended up being a little adventure: Apart from a damaged IC, I found a slight mistake in the 6502 card page (http://s100computers.com/My%20System%20Pages/6502%20Board/6502%20CPU%20Board.htm):
the "default" address of F8xx for I/O and EPROM access is reversed. The leftmost switch is A8, and the rightmost is A15, so the switch should be set to 0001111. The same mistake is in the first V1 photo: lucky me there is the schematic!
After half a day of schematic reading, EPROM programming, circuit probing (the extender board proved unvaluable, and also the book I'm reading, "Interfacing to S-100/IEEE696 computers" helped me a lot) I got the my basic console printing code to work, and got
out of the chicken-egg loop situation. I can now proceed fitting some useful code in my cpu card and start building other boards.
I now have the following roadmap for my system:
1. Wire the keyboard
2. Install a 6502 Monitor
3. Build the RAM/EPROM board and put 1Mb of ram inside the system (To be partially tested using the 6502 monitor)
4. Build the Z80 CPU card
5. Build the Serial IO card (to download binaries in ram through the serial port)
6. Build the IDE board... and hopefully start an OS
7. ??? Need to choose between 8086 or any other board I'll get in the meantime...
Thanks to John and Andrew for designing the boards, and thanks to everyone else who helped me in my build and replied to my pestering questions!
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