Using Device Memory

[jamesfkelly]

I've been struggling trying to use the device memory along with index registers in a Q00J PLC. For the longest time I did not think I was using the index registers correctly, as there was never any change in the output of my move, no matter how many times I changed the code using the index registry. I eventually found, by accident of course, that the device memory is CLEARED whenever you reset the PLC. In hindsight, this make perfect sense. But I was making changes to the code, trying to find the problem, and downloading the new code and the Device Memory to the PLC at the same time. Then of course resetting the PLC to run the new code. Never realizing that the Device Memory had been reset. So, I have finally learned that I must first download the code and reset the PLC and only after the PLC has been reset can I download the Device Memory array. Most of you are probably already aware of this, but maybe this post will help someone who is stuck like myself sometime in the future. As is this such a simple kind of a problem, and one I never thought to ask/check into it at all. Anywho, I just hope I can give something back to this forum, since I've taken so much from it in the past 6 months. Cheers, James

[Crossbow]

In PLC Parameters, on the Device tab, you determine which addresses are backed up by the battery. The defaults are blank, so none. If you set areas to be retentive, then they will maintain their values after a PLC reset.

[jamesfkelly]

Cheers, that's fairly handy information.

[Goody]

lol, in my early days with mitsubishi, I uploaded a program from an 'A' series plc while it was running. I uploaded the program, the paremeters and device memory. I did some programming and then downloaded everything back, including the device memory - this put the machine somewhere else in the cycle and things went crash. I have only done THAT once :)

[MS10]

Hi Jamesfkelly, I am new to Mitsubishi PLC and having a bit of difficulties with the device memory. I am currently modifying a previous project written by my colleague. There are some values previously saved in the device memory and I have downloaded these to the PLC. The problem that I'm facing is, I can't seem to write a value to these device (for e.g. from the HMI). I am pretty sure it is due to the device memory that I have downloaded but I can't seem to erase this values either. I have tried using 'clear PLC memory' and 'format PLC memory' and monitor them at the same time. The devices values went to 0 after clearing (PLC is in STOP mode because I can't clear the memory when it is in RUN mode). Once I switch the PLC to RUN mode, the previous values came back. I have also tried clearing all the device values in the device memory to 0 and re-write it to the PLC. It says writing is complete but did not seem to write the 0 to the PLC. I double check by using 'read from PLC' and the old values are still there. My colleague once told me that Mitsubishi PLC does not seem to be happy with 'partial download' of the program. This is what I did - I only downloaded 5 out of the 20 program that I have in the project. I wonder if this is the cause of the problem? I can't download them just yet as I have to make sure that all the device is within the range, etc (as mentioned before I am modifying an existing project). I would appreciate if you can help me in clearing this device memory from my PLC. Thanks, MS10

[Crossbow]

If putting the PLC in RUN overwrites the values, then they are clearly being written from within the PLC program. Format PLC Memory erases the PROGRAM MEMORY. Clear PLC Memory erases the data registers (and file registers if checked).