Description:
If the length of the diagnostics message of a diagnostics signaling DP slave is exactly 6 bytes, then there is no OB82 call, no corresponding diagnostics buffer entry and the EXTF LED remains unaffected.

Until now this problem has only occurred with Festo valve islands. Here, only the message of the outgoing diagnostics has a length of 6 bytes, so that incoming diagnostics are displayed (OB82 call, diagnostics buffer entry, EXTF LED), but not outgoing diagnostics messages (i.e. EXTF LED remains set and outgoing diagnostics cannot be evaluated in the user program).

A diagnostics alarm is caused, for example, by a load voltage failure on a DP slave (e.g. through guard doors being opened). The EXTF LED lights here however even after the load voltage has been restored on the slave.

This concerns the following CPUs:
 

CPU	Order number	Product release	Firmware
CPU 315-2DP	6ES7 315-2AFx3-0AB0	01	V1.0.0
CPU 316-2DP	6ES7 316-2AG00-0AB0	01	V1.0.0
CPU 318-2	6ES7 318-2AJ00-0AB0	03	V1.1.0
CPU 412-1	6ES7 412-1XF03-0AB0	01	V1.1.0
CPU 412-2	6ES7 412-2XG00-0AB0	01	V1.1.0
CPU 414-2	6ES7 414-2XG03-0AB0	01	V1.1.0
CPU 414-3	6ES7 414-3XJ00-0AB0	01	V1.1.0
CPU 416-2	6ES7 416-2XK02-0AB0	01	V1.1.0
CPU 416-3	6ES7 416-3XL00-0AB0	01	V1.1.0
CPU 417-4	6ES7 417-4XL00-0AB0	03	V1.1.0
CPU 417-4H	6ES7 417-4HL00-0AB0	03	V1.1.0

What causes this?
If there is diagnostics data on a DP slave (e.g. load voltage failure), the DP slave signals this to the DP master. The master then requests the diagnostics data from the slave. This diagnostics data consists of a standard part 6 bytes long and possibly an extended diagnostics part. The structure of the standard part is specified by the PROFIBUS DP standard.

Now the following problem arises on a CPU:
If diagnostics is signaled by a DP slave (incoming diagnostics), the operating system calls the OB82 -> EXTF LED lights. This event is entered in the diagnostics buffer of the CPU.

In the case of an incoming diagnostics (e.g. return of load voltage) the DP slave again signals to the DP master that there is diagnostics data. The DP master then fetches this diagnostics data from the DP slave. In the normal case the EXTF LED goes out.

Problem with the CPUs:
It can however happen that for incoming diagnostics a DP slave sends 6 bytes standard diagnostics + 6 bytes extended diagnostics. If the slave only sends the 6 bytes of standard diagnostics for the outgoing diagnostics, then this is not evaluated by the CPU. The OB82 is not called, there is no entry in the diagnostics buffer of the CPU -> EXTF LED doesn't go out even though the problem no longer exists.

Remedy:
The following overview includes the Entry IDs in Online Support where you can download an operating system update for the CPUs mentioned.
 

CPU	Entry ID
S7-315	7360491
S7-316-2	7360799
S7-318-2	7286150
S7-412	2792880
S7-414	2850229
S7-416	2858911
S7-417	2855123
S7-417-4H	6741018

There are two ways of determining how many bytes of diagnostics data a slave sends to the master:

• SIMATIC Manager:

1. In the SIMATIC Manager go to "PLC -> Diagnose Hardware".
2. Mark the relevant slave.
3. Press the "Open station online" button.
4. In the "DP slave diagnostics" tab, press the "Hex display" button.
5. The window that now opens displays the diagnostics data of the slave.

• Recording of the data traffic with the PROFIBUS monitor (Amprolyzer):

1. Trigger diagnostics messages (e.g. trigger event: SSAP 3C).
2. The diagnostics data is located in the data unit of this diagnostics response message.

Sample Amprolyzer recording:

Incoming diagnostics:

6 bytes standard diagnostics + 6 bytes extended diagnostics

S7teleg6b_P4_01.gif ( 2 KB )
Fig. 1

Outgoing diagnostics:

Only 6 bytes standard diagnostics

S7teleg6b_P4_02.gif ( 2 KB )    
Fig. 2

The result of this is that the EXTF LED doesn't go out on the CPU.

Keywords:
Hardware compatibility, Updates