Basic questions for RS232/422/485 & Modbus

[OnlyOne]

Hello,

i have to write some libraries for four types above.

But, i only have a normal windows-computer with a normal serial-connection.

Do i see it correct that can then only make "RS232" with this and that 422 amd 485 are then "special" serial-cards?

So for me it seems that 232/422/485 are three different hardware-types.

And only Modbus is a software-protocol that can be created with labview.

Is this correct?

Thanks for help

[crossrulz · Accepted solution]

RS232/422/485 are hardware specific.  Many RS422 UART cards out there will also handle RS485.  Luckily, most of these cards just show up as a COM port, so the software is the same for all 3.

According to Wikipedia, most Modbus devices use RS485 as the hardware layer.  I will admit that I have no exprience with Modbus, so I'm not going to offer any advice on it.

[smercurio_fc]

You will definitely need either a plug-in card or an external module to get RS-422 and RS-485. Nowadays most computer don't even have serial ports anymore, and those that do are RS-232. RS-232 is single-ended. RS-422 is differential, and was designed to extend the range of RS-422. RS-485 was an extension that allowed for true multi-drop applications (where you can have many devices on a bus, and any one could be transmitting/receiving).

From a software perspective, as crossrulz indicated, it would all appear as COM ports.

[MarcoMauri]

Concerning MODBUS,

you can find a Labview library here:

http://zone.ni.com/devzone/cda/epd/p/id/4756

It's old but does its work...

And here a good tutorial on this protocol:

http://www.ni.com/white-paper/7675/en

Regards,

Marco

[S1ack]

You can keep the single RS-232 serial port, and get an external converter for 422 and 485.

[Harry.W]

Marco,

I just downloaded the library zip file and there are folders named 71, 82, 85, 86. I have a labview 2010. Which one works for me?

Thanks

Rgds,

Harry

[crossrulz]

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Harry.W wrote:

I just downloaded the library zip file and there are folders named 71, 82, 85, 86. I have a labview 2010. Which one works for me?

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Those folders are typically for the LabVIEW version.  Just use the 86 one since that would be the latest (LabVIEW 8.6).