RS485 -> USB adapter

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Lennart
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Posted by Lennart: Tue. May 8, 2012 - 12:38 PM
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Hi,

I've built an application where there is a Master unit talking to a Remote unit over RS485.
Master initiate all comm with Remote.

Now I want to let a PC have the role of the Remote.
So I need to convert RS485 to something that can be plugged into a computer.
And still preserve the bidirectional bus where Master initiate comms and
Remote collect data and also for some packets send data back to Master.
Would an adapter like this work?
http://www.ftdichip.com/Products...

Have a vague memory that USB communication need to be initiated from HOST side (PC?).
If this adapter won't work for what I need to do, can someone suggest another solution to communicate with PC bidirectionally where RS485 bus Master initiate comms and PC reply.

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Learning and Information, General Electronics
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mnehpets
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Posted by mnehpets: Tue. May 8, 2012 - 12:54 PM
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At the USB packet level, the communications are driven by the host end. However, the USB device can overlay different protocol models on top of it. For example, the standard UART CDC spec allows for asynchronous full duplex communications - so boths ends can communicate independently from the other.

FTDI use their own proprietary device protocol that I'm not familiar with, but it emulates a UART, so it should quite happily work as the "slave" end of your RS485 setup (I'm assuming you're sending UART framed bytes over your RS485 link).

- S

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Kartman
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Posted by Kartman: Tue. May 8, 2012 - 01:38 PM
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Lets not confuse USB host/ device with RS485 master/slave. The ftdi cable should work nicely. I've used the ftdi chips to do 485 comms many times and they work a treat as the chip itself knows when to turnaround the RS485 bus without any higher level intervention.

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Lennart
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Posted by Lennart: Tue. May 8, 2012 - 02:31 PM
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I thank you both for your assuring answers.

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