Default startup value for Network Inputs

Sorry if this seems a simple question, but I have not found the solution by reading the manual or from the forum.

I would like to set a default state to network input after a power outage or update. By default the state is always zero running the program first time. This should work so that when NI state is read, it shows the correct state.

I would imagine that setting the Variable Virtual Memory value attached to the NI at startup would be the way to go, but I have not figured out how to do that.

Thanks!

ixo65

When the LOGO! is switched on or restarted, all values in the VM memory are 0 because the VM memory is not remanent.

 Yes, this is indeed the default behaviour. Now I would like it to set the value to 1 on startup.

There's a startup flag M8. Is it possibe to make use of this?

From manual:
"The M8 flag is set in the first cycle of the user program and can thus be used in your circuit program as a startup flag."

WWEE

It's more difficult to do, but I once ran into a similar problem (reading network inputs takes a while after LOGO starts). An easier option is to read the NI state with a delay (On-Delay trigger) - if state of the network input is True for, for example, 2 seconds, then accept its state change).

...

 

 Thank you for the replies thus far! I'm using digital input/outputs.

I've figured out now that it's easy to set the value to 1 on startup. Simplest is connecting Status 1 (high) to Network output (digital). Obviously this will permanently lock the value to 1.

I can use Latching Relays where the trigger is M8 Initialization Flag, and it works great. However, again, Network Input value is locked as 1, and externally sending value 0 to Network Input doesn't work, because the Latching Relay keeps the state high and seems to override. What I can do now is use another Network Input to reset the latching relay, effectively gaining control of the first Network Input. However, this would effectively just split On and Off state into two Network Inputs.

Is it possible to give three different values to Network inputs using Network Output? Ie. 1, 0, -- or the third option: no value (no locking).

I'm very new at this, so it's all trial and error.

ixo65

A NI is a digital value. Digital values can only make two states: 0 or 1.

 I suppose I phrased my question wrong. Sorry. Since the NI state can only be 0 and 1, is it possible to set the NI value by multiple sources, where the external network command can override the original value 1 to the new value 0?

In other words:

When using diagrams, it looks like the NI is using "AND" logic, ie. if there is even one source setting value to 1, it will be 1. However, sending an S7 command externally, this is LATCH logic, since I send value 1, and it  stay as 1 until value 0 is set. Is it so that similar latching logic cannot be (easily) achieved by setting the value within the internal logic (soft comfort diagrams)? Ie. send value 1 until it's overriden by 0 by external S7 commands?

No, you can't connect multiple outputs to one input, at least that's not the correct way. For correct way you need an OR element.

Since you haven't said what version of LOGO you have, I can't make a proper diagram.But I'll give you an idea.

Network input (NI) connect to one input of OR element.

Off-delay functional block input Trg connect to M8 flag. Off-Delay otput to one input of OR element.

Off-Delay functional block input R (reset) connect to NI.

In parameters of Off-Delay specify a small timeout, for example 4-5 seconds (until network connection is established). If NI state is 1 before Off-Delay times out, then it resets Off-Delay timer and and it no longer interferes with normal NI operation.

In this way, you can manage with one network input (although the solution with an RS trigger and two NI inputs is not bad either).