Entry type: FAQ, Entry ID: 15364459, Entry date: 07/09/2015
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What restrictions are there for active jobs when communicating with "WR_REC"/ "RD_REC" and "RDREC"/ "WRREC" via PROFIBUS DP and PROFINET IO?

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Depending on the CPU used, the number of active jobs of the system functions and blocks "WRREC" SFB53/"WR_REC" SFC58 and "RDREC" (SFB52)/"RD_REC" (SFC59) is limited.

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.
 

System function/
system block

SFB 52 "RDREC"/
SFB 53 "WRREC"

SFC 59 "RD_REC"/
SFC 58 "WR_REC"

Explanation

Data record from DP slave, PROFINET IO device

 

Data record from DP slave

IM154 (ET 200pro),
IM151 (ET 200S),
IM147 (ET 200X)

4 jobs total (RDREC, WRREC, RD_REC, WR_REC)

CPU 312, CPU 313, CPU 314,
CPU 315, CPU 316

4 jobs total (RDREC, WRREC, RD_REC, WR_REC)

CPU 317, CPU 319,
CPU 318-2

8  jobs total (RDREC, WRREC, RD_REC, WR_REC)

CPU 41x 1)

8 jobs each per PROFIBUS DP segment and PROFINET IO system

CPU 121x

4 jobs total (RDREC, WRREC)

not available

CPU 151x

10 jobs total (RDREC, WRREC, RD_REC, WR_REC)











  
1) The number of simultaneous jobs on external PROFIBUS DP segments or PROFINET IO systems must not exceed 32 jobs per SFC/SFB.

Example
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).

Rules

  • 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.
    Example:
    When communicating with an FM 355 (4 channels parameterized) via the FMCS_PID block, 4 read jobs are occupied.

Note
The runtime of multiple instances running simultaneously can be longer than separate read/write jobs. 

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