Micro850 CCW - How do you NOT retain a variable on power cycle?

Hi All,

Hoping the community here can help as I'm new to PLC programming. The project I'm working on is using a Micro850 2080-LC50-24QBB and programming in ST. I have the program running mostly as needed, however, only just discovered in the manual that "Micro830 and Micro850 controllers retain all user-created variables" on power cycle.

Here's the thing. I do NOT want that behavior for all my variables. I am specifically implementing a power state machine, and I want the state variable of the state machine to reset to a known value when power to the controller is lost. I had assumed I could achieve this by just giving it an "Initial Value" which the variable would receive when power is restored and the program starts. Is there a way to achieve this functionality (have a user variable get written to say, 0, whenever power is cycled)?

Appreciate any pointers, thanks!

there should be a first pass system bit that is true for the first single scan after the PLC transitions to RUN mode. So that bit could trigger a routine that resets all the bits in the state machine.

__SYSVA_FIRST_SCAN - first scan bit

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drbitboy said:

there should be a first pass system bit that is true for the first single scan after the PLC transitions to RUN mode. So that bit could trigger a routine that resets all the bits in the state machine.

__SYSVA_FIRST_SCAN - first scan bit

_

Click to expand...

+1

In CCW, the "Initial Value" is what the variable defaults to when a fresh download occurs. Any changes made to the variable in the program during normal operation will be maintained through a power cycle.

I've used the variable mentioned by drbitboy multiple times for exactly what you are describing. As the name implies it is only true for the first scan, so you can use it by itself to trigger whatever power cycle initialization may be necessary.

This did the trick, thank you!