Using Multiple USB to RS-485 Adaptors

**kychristmas** · 03-03-2011, 01:24 PM

Personally, I use a Moxa 4-Port RS-485 card, but I recently ordered a Bulk-Lot of USB to RS485 converters for when the Connection Frenzy happens. The idea is to have a Converter that is pre-configured, wired, and tested for Renard so that the user can just plug in a straight through Cat-5 cable between the adaptor and the first Renard.

I had been asked about using multiples...

Can someone that uses one of these tell me if it is possible to use more than one of these simultaneously? Meaning, have get two or more RS-485 using multiples of these? In theory, it should work, but relying on theory is the same as assuming.

Kelly

**chelmuth** · 03-03-2011, 02:27 PM

My experience with the USB-485 Dongles is about 2 minutes old. But with that said as far as I can tell they are just like the USB-RS-232 Dongles.. I would say it's possible to use multiples.. The only caviat being that when you put one in a different USB port.. It changes Com port numbers.. IE.. I plugged the same dongle in to each of my USB ports on the computer and each time it came up as a different Com Port.. ie. Com4,5,6,7.. Now if I were to plug a different one in and do the same thing it would end up being 8,9,10,11.. So it will work people will just have to be concious of what they are plugging where.. if they accidently move or reverse them while moving something windows will add additional Com ports instead of re-activating the currently assigned ports. ie if I had 4 and they were arranged as 1,2,3,4.. If I accidently unplugged or reversed 2 of them it could end up looking like 1,3,5,6.. in this example I reversed what was origianally 2 and 4 and windows made new ports 5,6.. So in short it will work, but you have to be aware of what is happening and what you assign ports to in Vixen and understand how it could possible change.. where as the moxa cards are always in the same spot everytime.

Edit : Additionally it is possible to change them around manually in the device manager. If someone is comfortable enough to do it.. it's under the advanced settings for the com options.

**kychristmas** · 03-03-2011, 02:36 PM

That makes sense given that USB ports are essentially a big hub and there's really only one USB plane (for lack of the correct term).

Since someone asked, I wanted to know. I'll stick with my Moxa PCI card. Multiples would definitely not be something that I suggest or recommend for a new users anyway.

**ErnieHorning** · 03-03-2011, 02:37 PM

You can have up to 31 USB devices per controller. Most computers have at least two USB controllers. If you have anything inside the case that’s connected to the bus, it will be included in the total. The number of USB port connectors, is not the number of controllers. You may have 6 ports and only one controller.

**griffixdc** · 03-03-2011, 02:52 PM

if you read the "rs485 help" thread i started it explains that in there... it also explains that you cant essentially do it because the com port addressing wouldn't work it would send duplicate data to each split usb channel not different data ( like we want) ....but maybe if you can program a driver to recognize new ports from a port being split into multiple channels of ports then maybe it would work...but i have zero idea how to do that.

**dlovely** · 03-03-2011, 02:56 PM

Originally Posted by griffixdc

if you read the "rs485 help" thread i started it explains that in there... it also explains that you cant essentially do it because the com port addressing wouldn't work it would send duplicate data to each split usb channel not different data ( like we want) ....but maybe if you can program a driver to recognize new ports from a port being split into multiple channels of ports then maybe it would work...but i have zero idea how to do that.

Will actually work just fine. Each USB->Serial adapter will get a individual port address and show up in the system as COM#. No data ever gets split this way. USB specifications allow hubs to allow multiple USB devices, this has no affect on the RS485 data coming out of the converter.

**kychristmas** · 03-03-2011, 02:57 PM

Originally Posted by ErnieHorning

You can have up to 31 USB devices per controller. Most computers have at least two USB controllers. If you have anything inside the case that’s connected to the bus, it will be included in the total. The number of USB port connectors, is not the number of controllers. You may have 6 ports and only one controller.

That I didn't know. I assumed it was one controller. I added a USB 2.0 Card to an old Laptop that only had USB 1. That was the first time that I remember seeing multiple USB Controllers in the Device Manager.

**griffixdc** · 03-03-2011, 03:02 PM

Originally Posted by dlovely

Will actually work just fine. Each USB->Serial adapter will get a individual port address and show up in the system as COM#. No data ever gets split this way. USB specifications allow hubs to allow multiple USB devices, this has no affect on the RS485 data coming out of the converter.

ok never tried it out, just explaining what was explain to me

....although my desktop computer has 6 usb ports and only 4 show up in the drivers info but i can use all 6 successfully, can you explain that ? it it bewilders me. trying to assign a usb to parallel cable to bring my laserjet printer up and running.

**dlovely** · 03-03-2011, 03:13 PM

Originally Posted by griffixdc

ok never tried it out, just explaining what was explain to me

....although my desktop computer has 6 usb ports and only 4 show up in the drivers info but i can use all 6 successfully, can you explain that ? it it bewilders me. trying to assign a usb to parallel cable to bring my laserjet printer up and running.

You were wanting to split the 485 signal AFTER the adapter. That will just duplicate the data as the computer has only 1 port. Now when you put in a additional adapter you get an additional port to output data on from Vixan. No splitting signals so all data is original.

**griffixdc** · 03-03-2011, 03:18 PM

Originally Posted by dlovely

You were wanting to split the 485 signal AFTER the adapter. That will just duplicate the data as the computer has only 1 port. Now when you put in a additional adapter you get an additional port to output data on from Vixan. No splitting signals so all data is original.

ok heres my stupid question but it will help me learn.....so can i take a usb splitter 1 port in 4 out and then use that to have 4 different ports to feed different cables to rs485 converters while also having 4 separate signals not 4 duplicate signals?