Siemens SIMATIC ET 200SP System Manual page 127

Status of an asynchronous instruction
An asynchronous instruction shows its status via the block parameters STATUS/RET_VAL
and BUSY. Many asynchronous instructions also use the block parameters DONE and
ERROR.
The figure below shows the two asynchronous instructions WRREC and CREATE_DB.
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Figure 7-3
Distributed I/O system
System Manual, 12/2015, A5E03576849-AF
The input parameter REQ starts the job to execute the asynchronous instruction.
The output parameter DONE indicates that the job was completed without error.
The output parameter BUSY indicates whether the job is currently being processed. When
BUSY =1, a resource is assigned for the asynchronous instruction. If BUSY = 0, then the re-
source is free.
The output parameter ERROR indicates that an error has occurred.
The output parameter STATUS/RET_VAL provides information on the status of the job execu-
tion. The output parameter STATUS/RET_VAL receives the error information after the occur-
rence of an error.
Block parameters of asynchronous instructions using the instructions WRREC and
CREATE_DB as examples.
Basics of program execution
7.3 Asynchronous instructions
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