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Can any body explain urn-around delay in RS485 ?

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ITP

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RS485

Hi,

Can any body explain "turn-around delay" in RS485 Half duplex communication. How to take care of this delay.
Thank you
Itp
 

trace_ru

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RS485

I do, quite simply, by waiting a certain period of time to allow the line to settle. In my case the network consists of 32 units, all talking asyncronously.
Take a look at SNAP protocol. It's free.
http://www.hth.com/snap/
I use my own protocol but SNAP looks good.
trace
 

mgajo

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Hi speed up until error,
than return to working speed
 

Jason-dong

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Anybody has the workable model or source code?


Rgds,
Jason :)
 

ITP

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Hi trace_ru,
Thank you for your replay. You said all nodes are talking asyncronously, can you breif your protocol, and which rs485 IC you have used .

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trace_ru

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I use 75N176 as the driver (though I shojuld have used LTC1482 since it has carrier detect).
The protocol that I use is extremely simple:
<heared><length><source address><destination address><message><CRC>.
Messages require different types of replies (OK, not OK, status reply etc.) using the same packet format.
Nodes first listen to the network. When a period of inactivity is found, a node that wishes to talk to the network starts preudo-random wait cycle (related to the node address) and then if the line is still free - send the packet and waits for a reply. If no reply received, the transmit routine repeats 3 times before giving up.
SNAP has a better implementation but heavier (as far as the code is concerned).
trace
 

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