glitch
Veteran Member
I'm considering building up another project soon -- a bus-oriented 8-bit computer. This is sort of an extension of my 8085 SBC project. Having worked with several 8-bit bus architectures, I've naturally come up with what I think would be the "best" way to do it, from a hardware/hobbyist perspective...a combination of the S-100 bus, OSI-48 bus and Apple II bus. Functions would be on separate plugboards with a passive (well, actively terminated) backplane. I'd imagine there would be an 8085 processor board, RAM boards of some capacity, a UART board with boot ROM for monitor, et c.
While the first processor board would be an 8085-based one, being my favorite 8-bit processor, I'd really like to produce other 8-bit processor boards too. A friend of mine is interested in developing a 6502 board for it, and I'd like to build a NSC800 board as well. The system bus would be designed in a fairly generic manner -- 8-bit bidirectional data, 16-bit address, probably an IO/M control line, reset line, clock line, interrupt line(s)...I'm pretty sure I could fit it into a 50-line bus. To handle the problem of memory-mapped vs. programmed I/O, I have in mind a board that would map part of memory in the top 1K to I/O ports (asserting the IO/M line, et c.). This would allow boards that work with 8085 programmed I/O to be used with a 6502 processor board.
As to the hobbyist angle, like my 8085 SBC, the boards would be laid out in EAGLE CAD Lite, which is free for hobby use. I know I can pack individual functions onto the 3x4" area limit without too much trouble. The bus connector would be an IDC type, allowing use of cheap connectors for board interconnects (either stacking or backplane).
Does the world really need me to bother to do this though? The machine will get built anyway, as I want to do this for the learning experience, but I don't know that it's worth the time/money to have boards commercially etched when I can build them with wire-wrap or point-to-point construction. Hobbyists already have a few 8-bit kits to choose from -- the N8VEM SBC being a great example. I want to follow the designs of earlier systems though, mostly through limiting the functionality of each plugboard to a single task.
So, I guess the question is, does the world need/want another 8-bit kit?
While the first processor board would be an 8085-based one, being my favorite 8-bit processor, I'd really like to produce other 8-bit processor boards too. A friend of mine is interested in developing a 6502 board for it, and I'd like to build a NSC800 board as well. The system bus would be designed in a fairly generic manner -- 8-bit bidirectional data, 16-bit address, probably an IO/M control line, reset line, clock line, interrupt line(s)...I'm pretty sure I could fit it into a 50-line bus. To handle the problem of memory-mapped vs. programmed I/O, I have in mind a board that would map part of memory in the top 1K to I/O ports (asserting the IO/M line, et c.). This would allow boards that work with 8085 programmed I/O to be used with a 6502 processor board.
As to the hobbyist angle, like my 8085 SBC, the boards would be laid out in EAGLE CAD Lite, which is free for hobby use. I know I can pack individual functions onto the 3x4" area limit without too much trouble. The bus connector would be an IDC type, allowing use of cheap connectors for board interconnects (either stacking or backplane).
Does the world really need me to bother to do this though? The machine will get built anyway, as I want to do this for the learning experience, but I don't know that it's worth the time/money to have boards commercially etched when I can build them with wire-wrap or point-to-point construction. Hobbyists already have a few 8-bit kits to choose from -- the N8VEM SBC being a great example. I want to follow the designs of earlier systems though, mostly through limiting the functionality of each plugboard to a single task.
So, I guess the question is, does the world need/want another 8-bit kit?