Hello, i have very strange problem with S7-1212C DC/DC/DC, 6ES7 212-1AE40-0XB0, FW: 4.6

I'm using TIA Portal V18, and the device is configured properly. The wiring of the PLC is OK. In LAD even I made a very simple logic with just working OUTPUT(s) everything is OK (in online mode shows working, PLC output shows working).

The problem starts when I add NO contact and make this logic shown below.

Then go to online mode and the result is in s2.jpg, BUT the PLC leds work only Q0.1,Q0.2,Q0.3

When turning the switch to another position(%I0.1) then Q0.0 works.

In overall If I have duplicated outputs, in some of the parallels they don't work.

I did everything about compiling, downloading to the device, stopping CPU, and again starting but without result. 

Hi andrags,

According to your screenshot, you are writing twice to output %Q0.0. In monitor mode, you can see the state of the output as it is written by the PLC command per command. So you can see the two different states. But since the output is only written to the hardware once - at the end of your program cycle - the last state is written.

Kind regards
Stefan

Stefan Arcularius

Hi andrags,

According to your screenshot, you are writing twice to output %Q0.0. In monitor mode, you can see the state of the output as it is written by the PLC command per command. So you can see the two different states. But since the output is only written to the hardware once - at the end of your program cycle - the last state is written.

Kind regards
Stefan

What mean last state is written? I still don't understand why If I have duplicated outputs, in some of the parallels they don't work. If I have in parallel 1 (q0.0 & q0.1) and in parallel 2 have (q0.0 & q0.2)  and both have NO contact then when PLC runs q0.0 works only in one of the parallels :( 

Edit: when force it, runs that LED(output), but this is no solution just in proof that it is working 

Hi andrags,

Here is a simple explanation of how the PLC executes the programming shown in your screenshot:

1. Read %I0.0 and store its value.
2. Write the stored value to %Q0.3.
3. Write the stored value to %Q0.2.
4. Write the stored value to %Q0.1.
5. Write the stored value to %Q0.0.
6. Read %I0.0 and store its value.
7. Write the stored value to %Q0.0.

According to this explanation, the output %Q0.0 is written in both step 5 and step 7. However, since the result of all your code is transferred to the hardware at the end of the cycle, only step 7 affects your output. (Even if the values were written directly to the hardware, you would not notice the change from FALSE to TRU and back to FALSE because it happens in a very short time.)

I hope this helps you understand why it doesn't work. Of course, the exact solution will depend on your requirements.

Kind regards
Stefan

yes I have experience with C++ & PHP. When I used an Arduino I set and unset outputs by equal them to "1" or "0", but I supposed that TIA is smarter and (S) & (R) is only for MemoryBits.

Thank you so much.