El 22/12/2010 23:11, Chris Albertson escribió:
Again I don't care much what is used but I think we need
1) Reasonable speed
2) ALL cards should be peers with no "master"
3) in-band addressing
4) Small minimum size for the uP and low Flash memory footprint
Can "CAN" do this? I'm worried about #2 and #4. I don't have time to
read up on this right now and the Wiki article was not detailed enough
#2 yes. CAN is more oriented to variables, not to a master-slave
architecture. For example, in a car, if one node requires one variable
it sends a message with the message Id (11 or 29 bits, depending on CAN
version) and RTR bit set. The node that has that variable answer with a
message with the Id, RTR clear, and the variable value. Some nodes send
continuously messages. SAE-J1939 is a protocol oriented that way, simple
variable exchange.
#4 yes, for example AT91SAM7X128 (LQFP 100, enough Flash and RAM for
running as a quite complex CANopen node, for example)
But have in mind that CAN messages are limited to an 8-byte payload. And
CAN is not so complex, but more intended for its original application:
automotive message exchange. But it is very robust, and have gained a
lot of acceptance in industrial fields, where some automation protocols
have been designed to run specifically to run over CAN, like CANopen.
And also is used in spacecraft (ExoMars mission uses CANopen and CAN
message architecture, but with RS-485 physical layer instead of the
standard CAN automotive phisical layer).
Regards,
Javier
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