The "Signal System Error" function and the FB126 "PNIODiag" function block use the SFC13 "DPNRM_DG" system function to determine slave-specific diagnostics data.

The SFC13 system function works asynchronously, which means that the processing of the function can extend over several SFC calls and, thus, it may also span several CPU cycles. The effect of this, in turn, is that there may be several SFC13 jobs active per CPU at the same time. However, the number of SFC13 calls active simultaneously may not exceed a CPU-specific limit. The table below shows the number of jobs that may be active simultaneously.
 

CPU	Number of calls
S7-300	4
S7-318	8
S7-400	8

Table 01: Number of SFC13 calls active simultaneously

Consequently, you can use the functions mentioned above simultaneously. However, you must ensure that the maximum number of SFC13 calls active at any one time does not exceed the values specified in Table 1.

The download of FB126 "PNIODiag" is available in Entry ID: 26996747.

Note
More information about system function SFC13 "DPNRM_DG" is available in the manual "System and Standard Functions for S7-300/400 Volume 1 and Volume 2" in Entry ID: 44240604 and in the STEP 7 Online Help.