Read my eariler post - with the ripple loop scheme, you have very simple slaves. Signal with the 9th bit in uart. When a slave sees a rising edge on the 9th bit chain, it removes the following N bytes (info TO slave), and replaces them with it's messages (info FROM slave), and on these reply bytes it sets the 9th bit LOW. the next bytes simply pass thru, and now the next slave sees these clean bytes, as the first rising edge, so it removes/replaces them. and so on, right around the loop. eg, Slaves have 4 byte packets, master sends 40 bytes. Master sends > 40 bytes with 9th bit low. Starts message, 40 bytes with 9th bit high
1st slave 9th Bit IN = 40_Hi, OUT = 4_Low + 36_Hi 2st slave 9th Bit IN = 4_Low + 36_Hi, OUT = 4_Low + 4_Low + 32_Hi etc Master counts slaves, but inspection of the 9th bit stretch, so the frame size is usually > slaves.The slave needs to be ready with a small buffer, so what it sends could be from the previous frame (not this one ) if you need a lot of time.
Because every node runs its own baud, we found that having some small gaps between bytes ( extra stop bits ), gives the system more tolerance to baud rate creepages. ( ie your average baud must be less than the slowest actual baud of any node ) IIRC, this was good to appx 1 MBaud
There is no message-address info, or overhead, as the slaves position in the loop sets the 'address', adding /removing slaves can be automatic. Info is fully deteministic, and set by the frame rate.
I think Interbus has a similar scheme.
Suitable uC: The Atmel new AT89LPC213/4/6 series, Philips LPC9xx, or if you need serious analog operation as well, Silabs C8051F41x series....
-jg