There is a free windows modbus master that might help. The protocol is done and implemented in silicon available from multiple sources. The problem of custom chips is still there, but the price is reasonable, and there are at least a couple sources. Also, there is huge buy in as this is supposed to be the new home automation standard. Lucent, Cutler Hammer, and Microsoft, to name a few.
Data is context sensitive.
They make a powerline peer to peer networking solution for sharing data between 2 computers and sharing a printer. And they now have an open source policy . The flag must be escaped if it appears in the data stream. Ken Websters PIC16C74 serial port multiplexer . But I'm interested.