Siemens SIMATIC S7-1500 System Manual page 125

Relationship between REQ, STATUS/RET_VAL, BUSY and DONE during a "running" job.
Se q. no. of Typ e of call
th e call
1 First call
2 to (n - 1) Intermediate call
n Last call
Use of resources
Asynchronous instructions use resources in the CPU during their execution. The resources
are limited depending on the type of CPU and instruction; the CPU can simultaneously
process only a maximum number of asynchronous instruction jobs. The resources are
available again after a job has been processed successfully or with errors.
Example: For the RDREC instruction, an S7-1500 CPU can process up to 20 jobs in parallel.
If the maximum number of simultaneously running jobs for an instruction is exceeded, the
instruction returns error code 80C3 (lack of resources) in the STATUS block parameter. The
execution of the job is stopped until a resource becomes free again.
Not e
Lower-level asynchronous instructions
Some asynchronous instructions use one or more lower-level asynchronous instructions for
their processing. This dependence is shown in the tables below.
Please note that with multiple lower-level instructions, only one lower-level resource is
typically allocated at a time.
Automation system
System Manual, 09/2016, A5E03461182-AD
R EQ STATUS/RET_VAL
1 W#16#7001
Error code (e.g. W#16#80C3 for
lack of resources)
Not relevant W#16#7002
Not relevant W#16#0000, if no errors have
occurred.
Error code if errors occurred.
Basics of program execution
7.3 Asynchronous instructions
BU SY D ON E ER ROR
1 0 0
0 0 1
1 0 0
0 1 0
0 0 1
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