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from the Automation List department...
Communication Problem Between PC-PLC
PLCs and related questions. topic
Posted by Joska on 10 June, 2003 - 5:39 pm
I work with omron cx programmer v3.0, but since I
use laptop pc and USB-Serial converter UC-232A
always have communication problem between PC and
PLC.

Many thanks for solution!


Posted by Bruce on 12 June, 2003 - 4:59 pm
If you are using a "dumb" RS-232 to RS-485 converter, the problem could be due to unfaithful control of the RTS line of the converter by the USB serial converter. I had this problem with an Edgeport USB to Serial converter as it did not maintain the correct phasing between assertion of the RTS line and transmission of the serial data. I had to switch to a PCMCIA RS-232 port in my laptop to get true serial port equivalent performance.

If you are going straight to the PLC by way of RS-232 then it could be something else. You might still consider switching to a PCMCIA serial port converter instead.

bruce@sapia-inc.com


Posted by Anonymous on 12 June, 2003 - 5:10 pm
Good day sir!

i also experienced the same problem but with a SIMATIC 505 PLC. what i did was to lower the communication baud rate for both the laptop and the PLC instead of using a higher (default) baud rate. You could try this method as i heard that usb to serial converters sometimes don't perform well with faster baud rates. It worked for me but i am not sure if it will work for you.

Good luck and god bless.


Posted by David Wooden on 13 June, 2003 - 11:25 am
Things to try:

1) Reduce the baud rate.
2) Increase the response time-out.
3) Reduce the frame length.

You could also try the Omron USB to serial converter. (Part number is
CS1W-CIF31)

Best of luck,

David Wooden
Senior Software Engineer, Systems Integration
TAS Division of Omron Electronics LLC
Office: (847) 884-7034 Extension 432
Fax: (847) 884-9383
E-mail: david.wooden@omron.com


Posted by BobB on 16 June, 2003 - 8:41 pm
I could not use the USB/232 converter that came with my HP laptop (RTS problems). Bought a Wiretek brand and it works OK.

Still have problems sometimes with both Syswin and CX-Programmer. I have a fairly long 232 cable so I can get clear of bigfooted electricians on site when commissioning. I have found that if there is a loop in the cable (crossover) I have trouble. Sometimes up and down loading takes 4 or 5 goes with a large programme. If you can afford it, buy a PCMCIA serial port. They are more reliable. Also. keep your cable short. A good PCMCIA/232 can be purchased from BB Electronics.


Posted by David Adams on 19 June, 2003 - 1:21 pm
We always had good success with long (400-500 ft) when we used RS422 for the cable and put converters on either end.

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