MACs and On Line Changes

[Colin Carpenter]

You learn something every day. I've been having a lot of problems recently doing online changes when talking in "transparent mode" through a MAC E900 to a Q2AS CPU. Small changes (address change or change the operation of a contact) seemed fine, but anything involving deletion or insertion of code in the compiled code (IEC Developer) would result in an odd error message and an inconsistent project, involving stopping the PLC and downloading the entire project to get back to a consistent state. That's not much fun when you're working on a running process plant, it involves lots of waiting around and setting manual over rides on solenoids etc., just to get to a point where I can stop the PLC. I just assumed it was a Mitsubishi bug and kind of learned to live with it. Normally, I can't see the MAC screen when I'm doing this, but the other day, I happened to have one on the bench and noticed that whenever the online edit failed, the MAC screen showed a Comms error for a while, which intrigued me. So today I sent off an E-Mail to those nice people at Beijers, and they replied that if you edit the properties of the PLC driver (in peripherals section of E-Designer), you can increase the time out value from the default 2 secs up to 10 secs. This I did, and lo and behold, I can now do online edits without problem. It seems that the PLC stops communicating with the MAC while it's doing the online edits, and this is what causes the comms error and the glitch. E-Designer will let you set up to 10 secs as timeout, but you can do it in the MAC screen and set at least 20 secs (or maybe more) using the buttons on the screen to set the value. I've been using MAC software for 10 years or so, and never knew you could do that. Many thanks to Beijers

[Goody]

As usual Colin - thank you for that. I like to store all these gems somewhere in my head. I used to have that same problem with gppwin (and never cured it either) when I upgraded to GX dev it went away. :)

[Supporter]

Hi, What really happens is that when you do an online change that involves adding/removing code the programming software needs to move around sections in the memory of the PLC. This can be a bit time consuming and therefore the terminal may not receive an answer for a while. Since the default value is 2 seconds then there is a large risc that the terminal does not receive an answer for 2 seconds - if this is the case the terminal will believe that the connection is lost between the programming software and the PLC and therefore abort the connection and return to normal polling-mode. When you increase the time out the HMI will wait for an answer for a longer while.