Siemens SIMATIC S7 System Manual page 190

Program instructions
7.2 Clock
Extended power outage effect on the CPU clock
See the S7-200 SMART system manual appendix A CPU specifications, for how long the
real-time clock can maintain the correct time during power outages.
A CPU initializes with the time values shown in the following table, after an extended power
outage.
Date
01-Jan-2000
Note
Compact serial (CRs) CPU models do not have a RTC (Real-time Clock)
You can use the READ_RTCX and SET_RTCX instructions to set the year, date, and time
values in compact serial (CRs) CPU models, but the values will be lost on the next CPU
power off-on cycle. On power-up, the date and time will initialize to January 1, 2000.
190
Time
00:00:00
Day of week
Saturday
System Manual, V2.3, 07/2017, A5E03822230-AF
S7-200 SMART