[time-nuts] Form factor

[Javier Herrero]

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

-- 
------------------------------------------------------------------------
Javier Herrero                            EMAIL: jherrero at hvsistemas.com
Chief Technology Officer
HV Sistemas S.L.                          PHONE:         +34 949 336 806
Los Charcones, 17                         FAX:           +34 949 336 792
19170 El Casar - Guadalajara - Spain      WEB: http://www.hvsistemas.com