Siemens SIMATIC S7-1200 Safety Programming Manualline page 32

3 Methods for Safety Programming
Create a data type for the data from the HMI to the safety program. Use this data
type in the HMI tags, in the data buffer for the safety program and in the standard
user program where the data is copied.
To add more tags to be written from the HMI to the safety program, merely modify
this data type.
Figure 3-13: Copying data from the HMI to the safety program in the standard user program
Safe signal transmission
Communication between the HMI and the CPU is not safe. Transferring safety-
related data requires measures that ensure the safe transfer.
This application example shows a suitable safety concept:
https://support.industry.siemens.com/cs/ww/en/view/67634251
Resetting safety functions
For resetting safety functions or acknowledging errors using an HMI, TIA Portal
provides the "ACK_OP" system block.
An acknowledgment consists of two steps:
1. Change in/out IN to value "6" for exactly one cycle.
2. Change in/out IN to value at input "ACK_ID" for exactly one cycle within one
minute.
This system block is an exception to the recommended data exchange.
In each cycle, the system block resets the "IN" InOut parameter to "0". If the data
from the HMI is copied in the standard user program, "0" is overwritten with the
value from the HMI in each cycle and the condition that the values are present for
exactly one cycle is not met.
Therefore, write the tag at the "IN" input directly from the HMI and set the safety
program priority higher than that of communication to avoid potential data
corruption.
Figure 3-14: "ACK_OP" system block
Safety Programming Guideline
Entry ID: 109750255, V1.0, 10/2017
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