Basics of program execution
7.5 Asynchronous instructions
S7-1500R/H redundant system
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System Manual, 10/2018, A5E41814787-AA
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 RD_DPARA.
①
The input parameter REQ starts the job to execute the asynchronous instruction.
②
The output parameter DONE indicates that the job was completed without error.
③
The output parameter BUSY indicates whether the job is currently being executed. When
BUSY=1, a resource is allocated for the asynchronous instruction. When BUSY= 0, the re-
source is free.
④
The output parameter ERROR indicates that an error has occurred.
⑤
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.
Figure 7-7
Block parameters of asynchronous instructions using the instructions WRREC and
RD_DPARA as examples.
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