PLC Scan

[sid 0]

I am working on a machine where scan time affects my process. I want to know that memory flags such as M0 are refreshed at the end of program scan or it is updated as soon as logic processing?

[Engineer Saab 0]

The M coils are are direct refreshing. As the update as soon as the PLC scans the rung and does not wait till the end of the scan. The X and Ys wait till the end of the scan until they are updated.

[FNMdeJong 7]

The normal scan of a PLC is like follow; 1st read inputs 2nd program execution 3rd write outputs All other devices than inputs and outputs are directly updated when used in the program.

[waynes 8]

An alternative would be to set your plc to a constant scan time. This way you should get the same results continuously. For FX set M8039 and set scan time duration in D8039. For Q Cpu use setup in GX Dev

[sid 0]

Ok, Thanks to everybody...