Greetings everyone,

I have one problem with my program (I am using S7 1214 DC/DC/DC). I am creating a program for measuring total time between some actions for three work shifts. Variables %MD1, %MD2 and %MD3 are used for total time. Time is measured with three TONR timers. Problem is that after the timer the variables are changing but when I monitor variables in tag table it doesn't change at all. Also, in further program these variables aren't changing. I have attached also a picture. In the main program %MD1 has a value of 32s961ms and in the tag table %MD1 has a avalue of 0ms. I can't figure it out where could be a problem.

Thank you

Hello.

All three variables you mention overlap with each other. Siemens PLCs work like a 8-bit processor.

Read in the system manual of the PLC how addressing works. You will then notice that the bits you use %M0.0 and so on, also falls in the same memory areas as %MD0 (from the picture).

To avoid this situation create your tags inside a global DB.

Bye.
- Dan

#dP

Siemens PLCs work like a 8-bit processor.

 That's not true. Memory is aligned at byte boundary, but CPU is 32bit.

jacek d

#dP

Siemens PLCs work like a 8-bit processor.

 That's not true. Memory is aligned at byte boundary, but CPU is 32bit.

Hello.

Your words leave no doubt. I was aiming for the same with the word "like".

I am intrigued about the architecture you mention. From where did you learn this? Is it the same for all the CPUs?

My guess would be that the architecture for the S7-1200 (32 bit?) and S7-1500 (64 bit?) would differ. Perhaps earlier S7-300 might be 16 bit (0.5 * accumulator size ?).

I welcome you to educate me on this matter.

Bye.
- Dan

Hello #dP,

S7 300/400:

 https://support.industry.siemens.com/tf/WW/en/Posts/82666

#dP

I am intrigued about the architecture you mention. From where did you learn this? Is it the same for all the CPUs?

My guess would be that the architecture for the S7-1200 (32 bit?) and S7-1500 (64 bit?) would differ. Perhaps earlier S7-300 might be 16 bit (0.5 * accumulator size ?).

We have to differentiate the two things - the S7 CPU architecture and underlying hardware (uP). Otherwise we are talking about apples and oranges.

From the STEP7 user point of view the S7-300 CPU is 32 bit. That's how its registers are exposed. If it's real hardware 32 bit or it's emulated doesn't really matter. Because there's its operating system between the user program and the uP.