Siemens CSM 1277 Safety Programming Guideline

3 Methods for Safety Programming
Safety Programming Guideline
Entry ID: 109750255, V1.0, 10/2017
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 Siemens AG 2017 All rights reserved
3.4 True & False
Regarding the use of "TRUE" and "FALSE" signals in safety programs, there are
two different use cases:
 Actual parameters on blocks
 Assignments on operations
Actual parameters on blocks
For S7-1200/1500 controllers, you can use the Boolean constants "FALSE" for "0"
and "TRUE" for "1" as actual parameters for interconnecting formal parameters
during block calls in the safety program. Only the keyword "FALSE" or "TRUE" is
written to the formal parameter.
Figure 3-4: "TRUE" / "FALSE" signals as actual parameters
Assignments on operations
To generate "TRUE" / "FALSE" signals for operations, proceed as follows:
8. Create two static tags, "statTrue" and "statFalse", of the BOOL data type.
9. Assign the default "true" to the "statTrue" tag.
10. Assign the default "false" to the "statFalse" tag.
In the complete function block, you can use the tags as reading "TRUE" and
"FALSE" signals.
Figure 3-5: Declaration of "TRUE" and "FALSE" signals

Siemens CSM 1277 Specifications

General

Product type designation	CSM 1277
Transfer rate	10/100 Mbit/s
Supply voltage	24 V DC
Operating temperature	-40 to +70 °C
Mounting type	DIN rail mounting
Type	Industrial Ethernet Switch
Safety Integrity Level	Not applicable
Input Voltage	Not applicable
Output Voltage	Not applicable
Protection Class	IP20
Number of ports	4
Protocols	Ethernet
Power consumption	3 W
Number of Inputs	0
Number of Outputs	0