RIBBBIT65 On Mini-ITX: The Before Times
I've been ruminating and mulling on the possibility of implementing the RIBBBIT65 in a Mini-ITX form factor. My goal for this is to fit the "CORE" and SystemIO functionality in a Mini-ITX footprint, make use of rear panel IO and front panel lights and switches, and be supplied by a standard ATX power supply connector.
My first pass at the design study was arranging paper cutouts on a cardboard Mini-ITX sized blank. I quickly discovered that I could not fit the myriad functions I wanted on a Mini-ITX board using PDIP ICs. This was the impetus for trying to implement the address decoding using an EEPROM. I then toyed with a few variations on the theme of mezzanine boards... putting the CORE and primary peripherals on the motherboard, and "secondary" peripherals on the mez... putting the main peripherals on the main board, and the CORE on a mez... I settled on putting the CORE on a mezzanine, in large part, because its conversation with the IO is isolated to 8 address lines, 8 data lines, and an AD line. Sure, you need clock, RW, IRQ and so on... but... that simplifies routing immensely on the motherboard. It also permits me to use the CORE mezzanine in other applications if I want/need.
Goals
My first goal was trying to make a CORE mezzanine board. I figured making that fit on something I could stack on a Mini-ITX board would be something of an accomplishment. It would also give me something solid and tangible I could design against.
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| PotatoCam view of r0.1 of the CORE mezzanine card for the RIBBBIT65 Mini-ITX |
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| KiCAD 3D render of in-progress r0.1 of the RIBBBIT65 Mini-ITX Motherboard |
Above is my second layout of the RIBBBIT65 Mini-ITX, and I think this might be the best I can do under the circumstances. I don't know if this version of the RIBBBIT65 Mini-ITX is ever going to go to manufacturing. There's just so many compromises. I wanted to at least do a PCB layout to get a sense of the issues I was facing. I may send it out to manufacturing just to validate the integration... work out any bugs before I switch to PLCCs and SMT, but I really think PLCCs for the WDC chips and SMT for the passives and jellybean logic is going to have to be the way forward for the Mini-ITX form factor if I'm going to fit everything I want on there.
The journey continues...
