Siemens SIMATIC S7-1500 System Manual page 337

Basics of program execution
10.5 Asynchronous instructions
Assigning calls of an instruction to a job
To execute an instruction over multiple calls, the CPU must be able to uniquely relate a
subsequent call to a running job of the instruction.
To relate a call to a job, the CPU uses one of the following two mechanisms, depending on
the type of the instruction:
• Using the instance data block of the instruction (for "SFB" type)
• Using the input parameters of the instruction that identify the job. These input parameters
must match in each call during processing of the asynchronous instruction.
Example: The instruction "RD_DPARA" is identified by LADDR and RECNUM.
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
②
③
④
⑤
Figure 10-7
336
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 executed. When
BUSY=1, a resource is allocated for the asynchronous instruction. When BUSY= 0, the resource
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 execution.
The output parameter STATUS/RET_VAL receives the error information after the occurrence of
an error.
Block parameters of asynchronous instructions using the instructions WRREC and
RD_DPARA as examples.
S7-1500R/H redundant system
System Manual, 01/2024, A5E41814787-AF