Since you use those ultra-costly Silabs parts with their ultra-costly analog features that you don't even use, perhaps you could save some $$$ by using a more advanced CPU, e.g. a 100 MIPs ARM with 16 MB of SDRAM and a little FLASH. That would probably cost about $12 (MCU+RAM+FLASH+Crystal) in low-production quantity. There are lot's of 'em that would fit that model, and they typically have serial and parallel I/O, too, as well as a wide range of other more specialized comm hardware, e.g. ethernet, HDLC ...

RE