Saving test bit status on power failure

[BOWILLY]

I am new to Mitsubishi GX2 and GX3 software here at work. It is common practice to use an "M" memory bit as a temporary bypass. This is done by programming a N.O. bit and then toggling it on. It is also common practice to leave this in the program for extended periods - end of production run, product changeover, weekend etc. Is there a way to save the status of this collection of "M" bits on power loss and then reload the on or off condition on power-up? Recently got burned when power was cycled to a processor with such a bit active. On power-up , the software sets the bits's value to 0. Scrambling to find this undocumented change was an "adventure" .

 

[parky]

You can use the latch relay or a bit of a D memory (Q series)
You need to set the retentive range for those as in picture
Open up the parameters & there you can set the latch range of a number of bit/word types.

 

[BOWILLY]

Thanks, Parky. I figured there MUST be a way to use a latching bit. I'll have to play a bit and then take my findings to my superiors.

 

[parky]

Yes on the Q series you can also use D registers at bit value i.e. D10.0
It is a good idea to put many of those in the latch area i.e. D L etc. that way they are battery backed up R (Fie registers are different, you can create a file either in ram or SD card if fitted this also retains the status I often put a range of the D registers in the latch area for things like engineering or recipe variables so these retain the data on power down.