Acknowledge message using s7 protocol

Hi! I hope this question is relevant!

I use the S7 Protocol (via Sharp7 library) to get information about the state of blocks and manage them (for example, MonAnS - FB 1912) through the corresponding data blocks in my program. Simple write/read operations are sufficient for this. But I can't figure out how I can send an alarm acknowledgement request.

Hello,

pls specify more what alarm acknowledge you mean. I can imagine really more options/systems for this name of action...

The picture in the attachment illustrates what I want to implement programmatically - acknowledge a message about exceeding the limit (alarm).

For example, I used MonAnS (FB 1912). Unfortunately, I can't add another attachment, so I attach a link to the image with the state of the data block.

I can manage MonAnS via the corresponding data block, but I don't know how I can acknowledge alarms (which requests to send to the CPU over the S7 Protocol).

 The "System Software for S7-300,400 System and Standard Functions" document states the following (page 505):

The block-related message with Alarm_8P blocks which are used in S7-400 / PCS7 are not supported by Snap7 (as far as I know to this date). It works completely different to variable access. The message system uses only the message ids, so you'd need to know the meaning of every message id from your plc program.

I've programmed some functions for accessing the alarm-system based on libnodave for someone who needed this, but this was for the Alarm_S messages used in S7-300 plc. Alarm_S and Alarm_8P are also slightly different, with Alarm_S you can browse a list of active alarms with timestamps, as with Alarm_8P you can only browse that the message is active, but not the timestamp (thus the crossed out messages you sometimes see in WinCC), and other differences as well.

Thanks for your reply!

Can you recommend any materials for research on this issue? I looked at the examples of libnodave, but I didn't find an example of working with messages. 

ilepekhov

Thanks for your reply!

Can you recommend any materials for research on this issue? I looked at the examples of libnodave, but I didn't find an example of working with messages. 

 The query function for Alarm_S (alarmQueryAlarm_S) you can find here:

https://github.com/dotnetprojects/DotNetSiemensPLCToolBoxLibrary/blob/master/externalDlls/libnodave/nodave.c

You won't find anything in the official libnodave release. If you want to know how this works, you can create a Wireshark capture of the communication between AS and OS. I've written the S7comm dissection part in Wireshark, it will show you the details if there is request/response/notification for the alarm system.

I continue to investigate the mechanism of message acknowledgment. I did a traffic dump in Wireshark and found that the message from the MonAnS block has the ID 0x00000008. But I don't understand how it is possible to determine that a message with this ID belongs to my MonAnS block, and not to any other one...

I expected the value of the EV_ID parameter of the ALARM 8_P block to be 0x00000008, but this is not the case

If you want to analyze this, I'd recommend to use the raw Alarm8_P block without the fancy PCS7 stuff around this. EV_ID is definitively the Message ID.

I've just checked online what the MonAnL block is doing. I see at ALARM8P_1.EV_ID the same value as in the Parameter MsgEvId1 of the MonAnL block, which is internally (but conditional) linked to ALARM8P_1.EV_ID.

Thomas_v2.1

If you want to analyze this, I'd recommend to use the raw Alarm8_P block without the fancy PCS7 stuff around this. EV_ID is definitively the Message ID.

I've just checked online what the MonAnL block is doing. I see at ALARM8P_1.EV_ID the same value as in the Parameter MsgEvId1 of the MonAnL block, which is internally (but conditional) linked to ALARM8P_1.EV_ID.

 Thanks for the idea! I will try using the ALARM_8P block separately.

I checked the value of the MsgEvId1 field of the MonAnS block: in the "@Actual value" column MsgEvId1 = 0x00000000, and in the "Actual value" column MsgEvId = 0x00000008 (matches the EventID of the message). But if I read programmatically the value of the MsgEvId1 field, I get the value 0x00000000.