STep 7: "PLC data invalid" in status bar

[stplanken]

Anyone seen this before? While monitoring networks with a particular FC call, I see this in the status bar: "PLC data invalid"; it doesn't show any data.

Other networks in the calling FC can be monitored fine, just the ones with that particular FC call can't be monitored. I am able to monitor the variables via the Address Info tab fine. The FC in question has an elaborate interface, there are some 50 tags.

This is Step 7 5.5, CPU is a 319. This FC's interface is quite elaborate, about 50 or so tags. Monitoring has never been an issue until now. It does the same on a different engineering station. However, monitoring is not an issue on a different system that uses a 318.

 

[stplanken]

Just to follow up on m own post. It appears to be a limitation of the 319. I just set up a spare 318 and 319, and only loaded the FC with the elaborate interface (which uses a total of 61 bytes in the form of a mix of bool/int/dint), then called this from OB1 using dummy TEMP tags. With the 318 monitoring works. With the 319 I see the same "PLC data invalid" message in the status bar.

 

[Bratt]

The 318 is an oddball of the 300 series cpus's. Its built like a 400 cpu so that might be the reason for the 318 cpus to behave differently.

I think the 300 series has a PDU size of 240 and the 400 series have 480. PDU is max size of one message from the CPU to the PC

 

[Thomas_v2]

Have you a 318 or a 319 in your hardwareconfiguration?
The CPU of the 318 is different to the CPU of the 319.
The 318 is inside more a S7-400 than a S7-300. For example, the 318 has 4 accumulators, the 319 has only 2 as all other S7-300.

When you go online in a program block, the Simatic manager requests the status registers (accu1, accu2, db1, db2, etc.) for the code block you are viewing. Maybe the Simatic manager requests accu3 and accu4, but the CPU denies this, because it hasn't accu3 and accu4.

 

[stplanken]

I have both: one system with a 318, the other one a 319. The project with the 319 had its 318 CPU replaced with a 319 as it was running low on memory (exactly one year ago, actually). One of the things I did then is ensure that none of the code relied on the presence of accumulators 3 & 4. The FC being called mainly consists of simple ladder logic. I am wondering if this is a similar limitation as the maximum number of tags the 319 can monitor in a variable table. (For the 319 this number is smaller than that of the 318.)

 

[Thomas_v2]

I would check the firmware version of the CPU. There were some issues regarding to a large number of block parameters.

https://support.industry.siemens.com/cs/ww/en/view/23992548

 

[stplanken]

The latest firmware is 3.2.11. Just updated the spare 319, but it doesn't make a difference. As a test, I removed 9 integers and 9 double integers from the interface declaration. Obviously, the block wouldn't function anymore, but this was a test.) Now I was able to monitor the FC. Not sure where the cutoff is, but I am sure some undocumented limit is exceeded.

 

[Thomas_v2]

Normally the Simatic manager asks the CPU capabilities via SZL requests when going online. You can view whats going on with Wireshark when you go online via Ethernet. I've written the S7 protocol plugin for Wireshark ;-)
But there are some undocumented fields, especially in SZL ID 0x131 index 2, which contains informations about the communication capabilities for test functions.

 

[stplanken]

Interesting, Thomas. Do you happen to have a link or so with more info for SZL ID 0x131?

 

[Thomas_v2]

Interesting, Thomas. Do you happen to have a link or so with more info for SZL ID 0x131?

You find the SZL (or SSL) information in this documentation:
https://support.industry.siemens.com/cs/ww/en/view/44240604

But Siemens removed some interesting SZL IDs in newer documents.
However, it doesn't help to fix your problem.

 

[stplanken]

Thank you! (I knew I had seen it somewhere, couldn't find it.)