Serial IO RS-232/422/485

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Guest

Hi,

Hopefully this is a pretty basic question. I need to perform serial IO using
VB.Net (VS2005/Framework 2.0) but the devices I communicate with can be
either RS-232 or 422/485. Is this a concern to me as the programmer, i.e.
does the UART or whatever handles the electrical side of things or do I need
to be aware of the type of connection being made a program accordingly. I
know I need to use System.IO.Ports.SerialPort but does this only support
RS-232. I can't find anything in the documentation that says if its RS-232
specific or not.
TIA - Peter
 
Peter said:
Hi,

Hopefully this is a pretty basic question. I need to perform serial IO using
VB.Net (VS2005/Framework 2.0) but the devices I communicate with can be
either RS-232 or 422/485. Is this a concern to me as the programmer, i.e.
does the UART or whatever handles the electrical side of things or do I need
to be aware of the type of connection being made a program accordingly. I
know I need to use System.IO.Ports.SerialPort but does this only support
RS-232. I can't find anything in the documentation that says if its RS-232
specific or not.
TIA - Peter
Click to expand...
You do not have to worry, in simple terms they are just different
electrical connections. Unless you have some special PC you will need an
RS232/485 converter but that is just some hardware.
 
Hi Jack,
You do not have to worry, in simple terms they are just different
electrical connections. Unless you have some special PC you will need an
RS232/485 converter but that is just some hardware.
Click to expand...

Firstly, thank you for the very prompt response.

So, if I understand you correctly, if the device is not RS-232 I have to put
a hardware convertor on the line (before my serial port) that converts
RS-422/485 to RS-242.

Is this correct?

Cheers, Peter
 
Hi,

The UART is simply hardware that sends and receives serial (asynchronous)
data. It knows nothing about the physical connection or requirements.

How you handle RS-485 depends on the protocol AND on the actual device in
use. However, RS-422 needs no special knowledge -- RS-422 is
point-to-point, balanced transmision, and from a software standpoint is
identical to RS-232. RS-485 (like RS-422 is balanced), on the other hand,
may support multipoint communications, either half or full-duplex. If you
are using RS-485 for multipoint communications, your software needs to be
tailored to the task.

If your RS-485 connection is only between your PC and a single device, then
your code may need nothing special, if you employ a 4-wire connection. If
you use a 2-wire connection, then there is more work to be done, even so.

BTW, I have additional information on this in my book (see below).

Dick

--
Richard Grier, MVP
Hard & Software
Author of Visual Basic Programmer's Guide to Serial Communications, Fourth
Edition,
ISBN 1-890422-28-2 (391 pages, includes CD-ROM). July 2004, Revised March
2006.
See www.hardandsoftware.net for details and contact information.
 
Hi,
So, if I understand you correctly, if the device is not RS-232 I have to put
a hardware convertor on the line (before my serial port) that converts
RS-422/485 to RS-242.
<<

You need a RS-232 to RS-485 (or RS-422, which is similar, but not the same)
to convert voltage levels and to convert from single-ended (RS-232 on your
PC) to a balanced connection on your device if you use the serial port built
into the PC.

There are USB RS-422/RS-485 adapters that do not need to connect to a
physical serial port. Likewise, there are RS-422/485 boards that might be
used, too. A common scenario uses the PC serial port (RS-232) and an
adapter, but (easier) is something like:
http://www.usbgear.com/USB-COMi-M.html or
http://www.sealevel.com/product_detail.asp?product_id=516, which may be
configured to do what you want (there are lots of manufacturers of similar
hardware.

Dick

--
Richard Grier, MVP
Hard & Software
Author of Visual Basic Programmer's Guide to Serial Communications, Fourth
Edition,
ISBN 1-890422-28-2 (391 pages, includes CD-ROM). July 2004, Revised March
2006.
See www.hardandsoftware.net for details and contact information.
 
Peter said:
Hi Jack,




Firstly, thank you for the very prompt response.

So, if I understand you correctly, if the device is not RS-232 I have to put
a hardware convertor on the line (before my serial port) that converts
RS-422/485 to RS-242.

Is this correct?

Cheers, Peter
Click to expand...
In general yes although there are some specialised motherboards which
actually have the converter built in.
 
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