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Thread: Help! Dnc problem with Mitsubishi Meldas 520AM

  1. #1
    koeitool Guest

    Default Help! Dnc problem with Mitsubishi Meldas 520AM

    Dear or Madam

    Our CNC machine controller is Mitsubishi Meldas 520am(very old), PC operation system is Windows XP. RS232 connection: CNC Machine---25pin---25 pin---converter---9pin---PC.

    I have no problem to send very very small NC programs to CNC machine using ConnectCNC.( Using Xon/Xoff flow control, baud rate 4800, data bits:7, stop bits:2, parity: even). Since the memory at machine side is very small (less than 100k), I try to use DNC, but don't succeed, with error "P460 TAPE I/O ERROR". ConnectCNC does not seem to care about whether the CNC machine is ready for receiving or not, and it just sends the NC program after the SEND button is pressed. It never waits for a Xon singal.

    The funning thing is that the machine can't receive a small NC program when I use " Wait for Xon" function in other software such as Cimco edit (same settings as ConnectCNC on both PC and machine sides).

    so my stupid questions are:
    Is the Meldas 520 using the same port for data receiving and sending?(There is only one port on machine).
    Which handshake is better for this old machine( Xon/Xoff or hardware handshake or no handshake)?

    Any suggestion will be appreciated.

    Thanks in advance.

  2. #2
    Join Date
    Sep 2007
    Thanked 1 Time in 1 Post


    I am not extremely familiar with the 520, but I am farily confident that one port is used to send & receive the data. Either hardware or software handshake should be sufficient for loading files. The correct wiring for a 9 pin to 25 pin connection can be found here -

    You have stated that you can send a small file using ConnectCNC using Xon/Xoff, but then state in the next paragraph that "the machine can't receive a small NC program when I use " Wait for Xon" function in other software such as Cimco". Are you saying that it works with ConnectCNC but not with Cimco?

    For most controls to run in the "DNC" mode, they must have a mode selection that is usually designatedas "Tape" mode. Does your control have this?

    Another consideration is that some of the older Mitsubishi controls counted the even parity bit as a data bit, which would require setting the CNC to 8 data bits with no parity, while setting the DNC software to 7 data bits and even parity.

    - -
    Best Regards

    Paul Sevin
    Ovation Engineering, Inc.

  3. #3
    cnctech Guest


    Another thing I would add to what Paul said is, A lot of older machines have trouble receiving data faster than 2400 baud for some reason. You might try your first settings except change the baud to 2400 and see if that makes any difference. You also might look into what people call a BTR board for your machine, it allows you to use an add on board with your control that stores your programs and feeds them into machine memory.

  4. #4
    9566317 Guest


    On your CNC side setting for meldus controler is
    8 - 2 and even
    On you Computer side 7 -2 and even
    Drip can be done a 19200 baud but now is the stinker.
    If there a lots of little move the machine and buffer cannot react quick enough to stop the buffer overflow. No change in the Baud rate will stop this.
    I found that I needed to modify a drip feeding progam by putting in a "Trap" that stops transfer of data breifly to allow the machine to send the stop signal soon enough.
    If you get in touch with Mitsubushi they have a progam they say will work. I have never tried it.
    The problem is that the buffer is so small that when control asks for more data to fill the buffer it cannot send the stop signal quick enough before it overfills.
    Hope this helps

  5. #5
    TCA4570 Guest


    One thing, that I have learned, is that we keep decreasing our baud rates, to compensate for other problems.



  6. #6
    TCA4570 Guest





    prototype worked, out of the box!

    Maybe they can help?


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