Patrick said How do you know a transmission has started? How do you know what you "read" on the bus is not the bus being idle, but actually a 9bit word being present? How does the receiver know that the data is on the bus and valid?
Andy said how do you clock each word into your FIFO?
It’s quit straightforward really:) each 8051 (we are talking about two 8051s for now), connected to two FIFOs (ie. the same 9 bit bus connected to two FIFOs, but to input end(ie. write end) of one FIFO(we call it out FIFO) and to output end(ie. read end) of the other(we call it in FIFO).
When receiver polls empty flag of the “in FIFO” and realizes that “in FIFO” has some words in it, 8051 sends a read clock to this fifo and reads the content of bus and process it as I explained before (inspect 9th bit), if it was a command with let say with 5 words following it, the handling function clocks out those word sequentially (of course by sending read clocks) ,and I explained what happens next. When it wants to write a command it looks for full flag of fifo, if it was not full then 8051 updates content of bus("in FIFO" goes to high impedence mode of course) and sends a write clock to “out FIFO”. I hope It clears the problem.

Russel Said The problem was not the speed of transfer but rather how I had divided up the problem. The processing is the slow bit normally and may just offset the speed you gained using fifos. Good point, in my application one 8051s takes care of usb transmission and one other is a user interface(gathers information, responds to user when he or she plays with keypad, shows the result…) these two 8051s should know about each other because the user may use computer program or panel keypad. whatever the other has to change its parameters too. I want to use a protocol that doesn’t take precious processing time, the speed may not be very high for example 500 bytes/sec(15 hz), but the problem is each 8051 cannot wait till the other feels communication!

Michael said A long while back I devised a parallel type packet protocol that was used in the XTreeLink program. That’s great but how do you assess my protocol, what weakness do you think it has, especially I want to know what you think about cross checking feature and not to use supervisor chip, that nobody has addressed in detail yet ?

Regards
Ebrahim Vakilpour