What restrictions are there for active jobs when communicating with "WR_REC"/ "RD_REC" and "RDREC"/ "WRREC" via PROFIBUS DP and PROFINET IO?
System functions and blocks "RDREC" (SFB52)/"RD_REC" (SFC59) are used to read data records of a component (module) of a DP slave/PROFINET IO device.
System functions and blocks "WRREC" SFB53/ "WR_REC" SFC58 are used to write data records to a component (module) of a DP slave/PROFINET IO device.
Depending on the CPU used, the number of active jobs of the system functions and blocks "WRREC"/"WR_REC" and "RDREC"/"RD_REC" is limited.
The following table provides information about how many active jobs of the system functions and blocks "WRREC"/"WR_REC" and "RDREC"/"RD_REC" your CPU supports simultaneously.
1) The number of simultaneous jobs on external PROFIBUS DP segments or PROFINET IO systems must not exceed 32 jobs per SFC/SFB.
With a CPU 414-2DP, a maximum of 48 jobs per SFC/SFB can be executed at the same time (8 each on the two PROFIBUS DP segments that are connected to the integrated interfaces of the CPU, and 32 on external PROFIBUS DP segments and PROFINET IO systems).
- There are no restrictions for simultaneous jobs in the subracks (CR, ER). The SFCs run synchronously via the backplane bus. Any number of synchronous SFCs can be called.
- If you are operating multiple communication partners on the PROFIBUS network, then please make sure that never more than the specified jobs are active at the same time. Here one SFC/SFB can run several CPU cycles long.
- The restrictions listed in this entry for the active jobs of the system functions and blocks WRREC/WR_REC and RDREC/RD_REC also apply to the blocks that call these system functions and blocks internally. These include the blocks FM_CS, PID_FM and FMCS_PID, for example.
When communicating with an FM 355 (4 channels parameterized) via the FMCS_PID block, 4 read jobs are occupied.
The runtime of multiple instances running simultaneously can be longer than separate read/write jobs.