Erik

I read your response to one of the other postings and made a reply to it there but thought I shoudl start a new thread as it is drifting off subject.

I read up on the J1708 and I think that it looks great, on some of your other postings you seem not to like it that much. from what I have read (not a lot, the Nat App Notes and the Datasheet for the DS36277) it appears to be a drop in replace mend for the normal RS485 chips with the only changes being.

1, /RE is always held low (why don't the just do this in the IC?)
2, /DE is inverted from the RS485 chip so my uC will have to invert that port from normal
3, Termination of the BUS is not quite the same as it has more EMC filtering on it, and termination resistors are not required.

The question is then, How do I check (using the uC only - read other post using 555) whether the bus is busy - you mentioned in one of your other posts that you were looking for a RX in progress interrupt, this is what I would like to do and even using the J1708 I still can't see how you would do it without using a timer or counting from the RI to make sure that the byte had finished.

J1708 would avoid bus contention - assuming you also Rx'd back what you sent out on a bit level basis to make sure that another device wasn't pulling the bus low when you were sending a high is this correct?

The app note states the following
1, 20 devices
2, 40m
3, 9600bps

Have you had any other experiences more closely related to the RS485 limits, 32devices, 1200m, upto 10MBps (dependant on factors of course)

Sorry if it doesn't make to much sense, tell me if I am too vague and I will define the questions a bit better (basically looking for other users experiences) and it is late Almost Tuesday already!


Regards

Marshall