Clock Memory Issue

Hello dongepure;

My experience with various families of S7 controllers has always been that the clock memory mechanism was locked to the CPU's reatlime clock, and is completely independent of the scan cycle. But I have no documentation on the subject since it is part of the Siemens basic design (and they don't share that kind of information).

The best I can offer is this link to a discussion on a similar subject, with inputs from more technically experienced members:

https://support.industry.siemens.com/tf//ww/en/posts/clock-memory/103172/?page=0&pageSize=10

You will find more links to the clock memory and scan time relationship on the forum, just search for them.

Hope this helps,

Daniel Chartier

Hello

Thanks for your response

Would like to explain in detail about issues we are facing

We were using 319F-3PN/DP PLC which was occupied more than 80% of memory and no profibus nodes were left to add any further devices in system.( plc scan cycle is 56ms)

So we decided to change 319F-2PN/DP with 416F/3PN DP along with Profibus card to connect further devices.In this scenario the same program from 319 downloaded in 416  which takes 80ms of scan cycle resulting in delay for 100ms pulse.

100ms edge pulse is not responding properly the counts are equivalent to more or less like 600ms because of which the process is malfunctioning.

With this 400 series clock pulse will not work if we are above 50ms??

Does it effect only 100ms pulse or also their is possibility of missing pulse for 1000ms edge pulse??

With current program the work memory is occupied only 6%

The execution cycle of the program is slower then the half of the pulse cycle, therefore it can't catch them.