RS485 2-wire auto - Linux support

L

Thread Starter

Leo

Hi all,

I have been trying for a while now to find a RS485 card/adapter that has "2-wire auto mode" functionality AND has full Linux support. Can anyone recommend such a device?

To date I have got my code talking to my sensors (RS485 modbus RTU) on my Windows machine but the main project requires that we use Linux, yet the few cards I have tried that have 2-wire auto mode functionality (in Windows) loose this functionality in Linux.

The current 'fix' is to use a windows machine to read from the sensors then pass the data to the Linux machine - this is rather horrible! Please help!

Thanks,
Leo
 
L

Lynn August Linse

Worst case use an external RS-232/485 adapter ... which has to be cheaper than a 2nd Windows PC :)Most of these can handle the auto 2-wire turnaround.

You may also want to consider spending a bit more and get some ground isolation, as RS-485 works -7v to +12v and tolerates ground noise & shifts which crash the average 'PC-class motherboard' with lots of 1.8v circuitry which will consider a 1/2 volt wiggle on a ground line.
 
Leo:

> To date I have got my code talking to my sensors (RS485 modbus RTU) on my Windows machine but the main project
> requires that we use Linux, yet the few cards I have tried that have 2-wire auto mode functionality (in Windows) loose
> this functionality in Linux.

the reason U lose functionality is that instead of providing the functionality in the hardware on the card, the manufacturer chose to include it in the Windows driver. since U're not using Windows, U don't have the functionality.

this is an old problem. i work with an old system based on QNX2 (now Qnx6/Neutrino, bought by Blackberry a few years ago, and now behind the latest Blackberrys), and the modems we were using had the autoanswer functionality moved from the card to the Windows driver. we were in the same position U are in; we approached the vendor, who gave us a DOS program and a binary file with a patch; the DOS program flashed EEPROM on the card to include the functionality. U might want to approach your vendor to see if they would be willing to do that (maybe even for free, but i doubt it). another approach would be to check linux sites to ask if anybody has a driver that will satisfy your requirements. there are lots of coders who might be willing to do the reverse-engineering necessary to write such a driver, but if the card is too complex, they might not be.

good luck!
thx,
tanstaafl
 
C

Curt Wuollet

You might also try poking around the comedi project and Linux machining sites for cards that have been used successfully. A careful study on Google can turn up conversations that lead to answers. I would think some of the multiport cards would keep everything in ROM. Thankfully, the Winjunk era is winding down, although I've seen rooms full of gear that is electronic waste only because the Windows half is obsoleted or not maintained. Someday soon, gear that isn't standalone or multisystem capable won't be economically viable.

Regards
cww
 
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