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need help in protocol implementation

 
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funmix



Joined: 27 Mar 2007
Posts: 33

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need help in protocol implementation
PostPosted: Thu Apr 26, 2007 10:30 am     Reply with quote
Hi everyone,

I wish to design a network with 485 network(rs232 function). I am facing difficulty to design the protocol.

protocol format : <start><address><dataLength><data><cs>

any idea? appeciate if some one can provide snippet code/ example working code.

thanks
PCM programmer



Joined: 06 Sep 2003
Posts: 21708

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PostPosted: Thu Apr 26, 2007 11:43 am     Reply with quote
Use the search page.

Search for: serial protocol

Here is a long thread about it:
http://www.ccsinfo.com/forum/viewtopic.php?t=25980&highlight=serial+protocol
funmix



Joined: 27 Mar 2007
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PostPosted: Thu Apr 26, 2007 6:17 pm     Reply with quote
Hi PCM,

Thanks for reply. Any example code to refer? i have read the thread, but i got no idea how to start.
jds-pic



Joined: 17 Sep 2003
Posts: 205

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PostPosted: Mon Apr 30, 2007 1:22 pm     Reply with quote
funmix wrote:
Hi have read the thread, but i got no idea how to start.


you start by defining how the nodes on the rs485 bus interact.

e.g.
is the protocol polled master/slave or peer-to-peer?
if the latter, how are collisions detected?
are the packets fixed or variable size?
if variable, what is the maximum size packet?
what is the allowable packet latency?
how are transmission errors detected and handled?
what happens if a node can't respond immediately?

asking for code when you have not defined even a simple set of requirements is just going to lead to a lot of confusion and round-and-round question/answer posts.

reread the entire thread that PCM linked to above and reread the document i authored and then posted in that thread.
http://losdos.dyndns.org:8080/public/pic-uC/cbus-protocol-spec-draft-rev1.pdf

consider the benefits and drawbacks of the example implementation i wrote. how is it similar to what you need? how is it different from what you need?

jds-pic
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