serial communications-mixed USB, RS232, RS485

[sylvester]

Hi,

I got a system with variuos serial instruments attached (RS232) and I also have some connected via USB. Now I got another instrument that runs on RS485. Now, do I have to equip all my RS232 instruments with one RS232-RS485 converter each and the PC with a USB-RS485 converter to run the whole system as a RS485 network? Or is it possible to have e.g. one RS485, three RS232, and two USB instruments connected to my PC and control all with the same Labview program? 

Thanks for help!

[Dennis_Knutson]

You can control all of the instruments in one program without changing the communications. I currently control up to 6 RS-232, 2 USB, 1 GPIB, and 10 cPCI instruments with ease. There is no limitation in LabVIEW as to how many instruments you can have connected.

[sylvester]

I know there is no problem with USB, RS232 or GPIB; my question was regarding a mixed RS232/RS485 system using VISA for control. If I addess COM ports with VISA, do these ports have to be all RS232 or all 485 or is a mixture possible?

[mikeporter]

As Dennis pointed out, LV can handle multiple devices like that with ease. The only time I would consider rearranging everything is if there are other circumstances (like having a PC with only one serial port or something) where having a single serial interface would be an advantage. As it is though, changing to a single port would only slow things down.

Mike...

[mikeporter]

The COM interface doesn't make any distinction between RS232 and RS485. They all just show up as a serial ports.

Mike...

[RavensFan]

I think you might have one problem with converting all of your RS-232 instruments to RS-485 and having them run on a single bus.  That is, when you put a message out of your PC on an RS-485 port all of the devices on the line will get it.  Devices with RS-485 built in probably have an addressing scheme (modbus, something proprietary, another industry standard) to know what messages to listen to and which to ignore.  An RS-232 device probably won't since it was designed to run on a single point to point type communication line.  It might get confused if it reads a command intended for another device.  Suppose it throws out some kind of error message on the line at the same time the correct device is sending out its response?

Now there maybe more specialized RS-232/485 converters that could abstract out an addressing scheme.  Kind of like those RS-232 multiplexers (2, 4, 8, or more 232 ports that connect to a single PC 232 port) that have some command codes to select which one you are talking to.

You would need all of the devices to have compatible communication protocols to have a shot at this working.

[Brian_Beal]

I'm not sure if your question was answered.  What you need to do is keep your existing instruments as they are, and add another com port that is RS-485 compatible.  The simplest way to do this is to get a USB to 485 converter.