pc to plc

Discussion in 'Programmer's Corner' started by ochoya, Oct 24, 2013.

  1. ochoya

    Thread Starter New Member

    Jul 27, 2012
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    am having a problem going online from my pc connecting to plc allen bradley type...any idea? tried changing cables in vain
     
  2. strantor

    AAC Fanatic!

    Oct 3, 2010
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    What Allen Bradley PLC? BE SPECIFIC. Different Allen Bradley PLCs communicate on different protocols, with different proprietary cables, and different settings in RSLinx. Some of the older PLCs require a special interface box that will ONLY work with an ACTUAL serial port (no USB>serial converter) and will also not work if your laptop OS is any newer than XP SP2. Also depending on the platform, there are two different software suites you might need; the lower end PLCs use RSLogix500 ($500 or so) and the higher end PLCs use RSLogix5000 ($2000-$12,000, depending on options). RSLogix500 will NOT go online with a logix5000 PLC.
     
  3. MaxHeadRoom

    Expert

    Jul 18, 2013
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    The interface you need if using the older SLC500 is the 1747-PIC.
    Max.
     
  4. strantor

    AAC Fanatic!

    Oct 3, 2010
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    That's the bastard that requires XP SP2 or earlier and ONLY hardware serial port. And it's used for SLC500, not earlier AFAIK. Supposedly you can use 1747-UIC (USB interface) but I've never tried.
     
  5. MaxHeadRoom

    Expert

    Jul 18, 2013
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    I also found that the RSlinx takes the serial port over, so if exiting and using another RS232 utility, you have to unload the RSlinx driver first.
    Max.
     
    strantor likes this.
  6. panic mode

    Senior Member

    Oct 10, 2011
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    well, that is true for default behavior after installation (to run as service) but one can turn it off. those unfortunate ones that had to use 1747-PIC will know that installing driver for it actually replaces windows RS232 driver. so even if you shut down RSLinx, your serial port remains unusable until you reinstall serial port driver. another issue with 147-PIC is that it was deriving power from RS232 port. in the old days when RS232 ports had +/-12V swings and could provide more than 10mA current on any pin, that was fine. But just like JDM/Ludipipo this no longer works with modern RS232 ports because they are all low power and voltage swings are much smaller. if you had to use it today, go for old PC with built in RS232, not add-on card or usb/serial converter.


    as others have mentioned, you need to specify at the very least processor type. different processors have different communication ports. normally each CPU will have at least one RS232 port, talking DF1 plus something else (or nothing). that something else could be DH485, DH+, Ethernet or another RS232 port.

    make sure to read datasheet and identify ports correctly.

    to communicate with RS232 port you need null-modem cable (1746-CP3, google it and you will find connection diagram). the problem here can be that CPU already has program and perhaps the port settings are changed to User mode (maybe to talk to barcode scanner or printer or modem etc.). in that case you first must change the port setting back to DF1 (by resetting CPU to factory defaults or using paper clip to push hidden button on powerup).

    datasheet will specify what the default port settings are.

    once you reach this stage, you can use RSLinx to configure driver for your connection. as mentioned, for RS232 you need DF1 etc. if you have PC with built in RS232 port (or one of good USB to RS232 converters) you may try AutoDetect feature. it basically expects from you to choose error correction type (such as CRC) and PLC type (such as micrologix, SLC or whatever) and then it tries all settings until correct ones are found (if possible).

    when successful, you will see PLC icon in the RSLinx browser (along with one representing your PC).

    at this point, all you need to do is open correct software (RSLogix5, RSLogix500, RSLogix5000 for example) and point it to correct node (one in RSLinx) using RSWho.

    then say upload, download or whatever floats your boat.

    note that even USB to RS232 converters that did not work with AutoDetect usually CAN communicate with PLC but.... you have to know the correct settings (baud rate etc.). if you don't you may have to try manually setting each and every one (and this is totally painful). this is where resetting CPU to factory default saves the day because you get to use settings mentioned in the datasheet.

    other types of port require different cable and sometimes adapter (such as DH+ card in PCMCIA format, an expensive and fragile bugger). if you use Ethernet, you need a way to specify address PLC is supposed to use before you can connect to it. this may be BootP (an older and lightweight predecessor of DHCP) for example (there is a BootP server you can use). I would usually just connect through DF1 to configure com ports of the CPU then change to Ethernet.

    soo.....

    before I spend entire evening describing every possible scenario and ways to connect to every CPU made by AB, how about you spill the beans and tell us the exact model and version of your CPU and RSLinx/RSLogix you have there?
     
    Last edited: Oct 24, 2013
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