RS485 -> USB adapter

Log in or register to post comments
Go To Last Post
4 posts / 0 new
Author
Message
Lennart
Lennart's picture
Level: Raving Lunatic
Joined: Sun. Oct 29, 2006
Posts: 2757 View posts
Location: Sweden
#1
Posted by Lennart: Tue. May 8, 2012 - 12:38 PM
  • 1
  • 2
  • 3
  • 4
  • 5
Total votes: 0

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.

Tags:

Learning and Information, General Electronics
Top
mnehpets
mnehpets's picture
Level: Resident
Joined: Wed. Nov 9, 2011
Posts: 943 View posts
Posted by mnehpets: Tue. May 8, 2012 - 12:54 PM
  • 1
  • 2
  • 3
  • 4
  • 5
Total votes: 0

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

Top
Kartman
Kartman's picture
Level: 10k+ Postman
Joined: Thu. Dec 30, 2004
Posts: 22139 View posts
Location: Melbourne,Australia
Posted by Kartman: Tue. May 8, 2012 - 01:38 PM
  • 1
  • 2
  • 3
  • 4
  • 5
Total votes: 0

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.

Top
Lennart
Lennart's picture
Level: Raving Lunatic
Joined: Sun. Oct 29, 2006
Posts: 2757 View posts
Location: Sweden
Posted by Lennart: Tue. May 8, 2012 - 02:31 PM
  • 1
  • 2
  • 3
  • 4
  • 5
Total votes: 0

I thank you both for your assuring answers.

Top