Hi all,

I need a switchable output that behaves as follows:

- One address to read & write via Modbus or S7 the state of the switch

- Additionally a digital input which will toggle the output

For this I created the attached solution which works fine in the simulator, both by pressing the I1 button or by writing 1 or 0 to VM0.0.

But when run on the real Logo 8.2, if I write a 1 to VM0.0 to turn on the switch, the logic starts to oscillate, i.e. the output is turned on, then immediately off and repeats indefinitely. So clearly the state is not propagated through the circuit fast enough and a VM0.0 keeps getting overwritten with every cycle?

Any ideas how I can fix this? It seems like a common thing to do and easily done with a "real PLC".

Another way to describe this problem from a "fresh start".. 

I have a network input (digital) which can be written by other devices to change state or read by them to observe state. Now I need to add a physical button to toggle the state.

I know I could split this into a state output and 2 auto-reseting network inputs, one to SET and one to RESET the value of the output. But this would mean changing many other devices to work with 3 variables (write set, write reset, read state) instead of using just one r/w variable like they do currently.

Hi, thanks for the example.. that network input is a pattern I am already using elsewhere but not what I need here.

So I currently already have a network input which is used by HMI and other devices by writing to it. They also monitor the value.

Now I need to add a physical button to it so the state can be changed without external HMI. Actually there are many outputs like this that now need physical buttons, not just one.. 

I really don't want to reprogram every HMI and other device from using one modbus read/write coil to a logic where state is read from one coil and then one or two momentary inputs are used to set the state.

Maybe this can't be done with Logo then? 

I think my problem is simpler than you imagine...

See picture.. simplest case.  Network input, written by another device like HMI. Add a momentary input to toggle value locally.

ixo65

By LOGO! is it not possible to toggle a digital network input bit with a physical input.

so it seems.. or even a flag or anything else..  It works in the simulator so I was hopeful.

it would be a wonderful block to have edge triggered write of a value to local variable memory.