Extended instructions
9.5 Interrupts
S7-1200 Programmable controller
System Manual, V4.2, 09/2016, A5E02486680-AK
427
If an error occurs, RET_VAL displays the appropriate error code and the parameter STATUS
= 0.
Table 9- 106 RET_VAL parameter
8090 OB does not exist or is of wrong type.
OB has no attached event.
If an attacker can access your networks through Network Time Protocol (NTP)
synchronization, the attacker can possibly take limited control of your process by shifting
the CPU system time.
The NTP client feature of the S7-1200 CPU is disabled by default, and, when enabled, only
allows configured IP addresses to act as an NTP server. The CPU disables this feature by
default, and you must configure this feature to allow remotely-controlled CPU system time
corrections.
The S7-1200 CPU supports "time of day" interrupts and clock instructions that depend upon
accurate CPU system time. If you configure NTP and accept time synchronization from a
server, you must ensure that the server is a trusted source. Failure to do so can cause a
security breach that allows an unknown user to take limited control of your process by
shifting the CPU system time.
For security information and recommendations, please see our "Operational Guidelines for
Industrial Security" (http://www.industry.siemens.com/topics/global/en/industrial-
security/Documents/operational_guidelines_industrial_security_en.pdf) on the Siemens
Service and Support site.
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