Initially I tried to keep things similar to RAMPS, then realized they were too many differences (e.g. 3.3V vs 5V, SPI on different pins, etc) so just assigned unused IO to connectors as convenient. I then realized I could get compatibility with SDRAMPS (SD card module) if nothing else, so Aux3 can be used with SDRAMPS. Maybe with BBB an SD card extension is less useful.
The rest are pretty much up for grabs. I followed a similar pattern to RAMPS, but don't expect any compatibility. As there is no standardization between controllers, expansion boards like the LCD/SD controller have a specific interface board for each controller. RAMPS-FD has clearance around the connectors to allow an adapter card to be plugged in over the connectors.
So I would try to collect up unused IO (if any!) on some connectors and put them convenient location for connecting via IDC connector, and not worry too much about compatibility. I mean, it's nice if you've got it, but it can constrain the design too much, and in practice most of the extension boards are designed for 5V, so are limited use.
[attachment 26113 IMG_0098_new.jpg]
ETA: the 4 pin I2C headers use the same pin out as RAMPS, as do the serial connectors which are designed to be compatible with a 6 pin connector FTDI use. The location on the board is not important I think.
The rest are pretty much up for grabs. I followed a similar pattern to RAMPS, but don't expect any compatibility. As there is no standardization between controllers, expansion boards like the LCD/SD controller have a specific interface board for each controller. RAMPS-FD has clearance around the connectors to allow an adapter card to be plugged in over the connectors.
So I would try to collect up unused IO (if any!) on some connectors and put them convenient location for connecting via IDC connector, and not worry too much about compatibility. I mean, it's nice if you've got it, but it can constrain the design too much, and in practice most of the extension boards are designed for 5V, so are limited use.
[attachment 26113 IMG_0098_new.jpg]
ETA: the 4 pin I2C headers use the same pin out as RAMPS, as do the serial connectors which are designed to be compatible with a 6 pin connector FTDI use. The location on the board is not important I think.