A word of advice regarding the Cross Bar. Make sure to plan for the MAX peripherals that you will want in the product. Then devise the cross bar settings needed to set that configuration. When you start coding then stick to that configuration.

Do all this _before_ you make any PC board artwork. If you add or take away peripherals later you have to be prepared for a fab spin in most cases since your peripheral I/O assignments will move around.

The SiLabs configuration wizard tool will help a lot in getting to an initial set of configuration code that you can follow in your firmware development.

I have devised spread sheet templates for each SiLabs part that I've used that looks pretty much like the CrossBar chart from the data sheet. I use this as my formal planning and and documentation of the pinning for any given design. It helps a lot to visualize the cross bar mechanism. The configuration wizard tool has also gotten much much better since I first started using Cygnal parts some 8-10 years ago. So my spreadsheets carry more of a documentation role than they do a design role.

To this day I still kind of wonder at the original decision to put these Cross Bar schemes into the chip. I think if they really wanted to be sophisticated about it that they would have made it as a full cross point switch with any peripheral targetable at any I/O pin. Even to this day, when I have to do some small 1-off job that requires an MCU with a quick design w/o spending a lot of time planning out the MCU pinning I usually drag out my C8051F226 eval board. That part does not have a cross bar and muxes the peripheral I/O out to pins in a fixed assignment much like the legacy 8051 did, although on even that part Cygnal decided to place legacy peripherals on different port.bit assignments than legacy mappings. (Maybe they do this stuff to make sure you read the data sheet).

Michael Karas