Siemens SIMATIC ET 200SP System Manual page 128

Basics of program execution
7.3 Asynchronous instructions
Summary
The table below provides you with an overview of the relationships described above. It
shows in particular the possible values of the output parameters if processing is not
completed after a call.
Note
Following every call, you must evaluate the relevant output parameters in your program.
Relationship between REQ, STATUS/RET_VAL, BUSY and DONE during a "running" job.
Seq. no. Type of call
of the
call
1 First call
2 to (n - 1) Intermediate
call
n Last call
Consumption of resources
Asynchronous instructions occupy resources in the CPU while they are being processed.
The resources are limited depending on the type of CPU and instruction; the CPU can only
process a maximum number of asynchronous instruction jobs simultaneously. The resources
are available again after a job has been successfully completed or processed with an error.
Example: The instructions RDREC and WRREC can each be called 10 times with different
instances. The number of parallel running jobs per instruction is therefore limited to 10.
If the maximum number of simultaneous jobs for an instruction is exceeded, the instruction
returns the error code 80C3 (lack of resources) in the block parameter STATUS. The
execution of the job is stopped until a resource becomes free again.
Note
Lower-level asynchronous instructions
Several 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 occupied.
128
REQ STATUS/RET_VAL
1 W#16#7001
Error code (for example,
W#16#80C3 for lack of
resources)
Not rele- W#16#7002
vant
Not rele- W#16#0000, if no errors
vant have occurred.
Error code, if errors have
occurred
BUSY DONE
1 0
0 0
1 0
0 1
0 0
System Manual, 12/2015, A5E03576849-AF
ERROR
0
1
0
0
1
Distributed I/O system