97BPLC concepts
4.1 Execution of the user program
S7-1200 Programmable controller
System Manual, 11/2011, A5E02486680-05
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Diagnostics buffer
The CPU supports a diagnostic buffer which contains an entry for each diagnostic event.
Each entry includes a date and time the event occurred, an event category, and an event
description. The entries are displayed in chronological order with the most recent event at
the top. While the CPU maintains power, up to 50 most recent events are available in this
log. When the log is full, a new event replaces the oldest event in the log. When power is
lost, the ten most recent events are saved.
The following types of events are recorded in the diagnostics buffer:
●
Each system diagnostic event; for example, CPU errors and module errors
●
Each state change of the CPU (each power up, each transition to STOP, each transition
to RUN)
To access the diagnostic buffer, you must be online. Locate the log under "Online &
diagnostics / Diagnostics / Diagnostics buffer". For more information regarding
troubleshooting and debugging, refer to the "Online and diagnostics" chapter (Page 640).
Time of day clock
The CPU supports a time-of-day clock. A super-capacitor supplies the energy required to
keep the clock running during times when the CPU is powered down. The super-capacitor
charges while the CPU has power. After the CPU has been powered up at least 24 hours,
then the super-capacitor has sufficient charge to keep the clock running for typically 10 days.
The Time of Day Clock is set to system time, which is Coordinated Universal Time (UTC).
STEP 7 sets the Time of Day Clock to system time. There are instructions to read the
system time (RD_SYS_T) or local time (RD_LOC_T). Local time is calculated by using the
time zone and daylight saving time offsets that you set in the CPU Clock device
configuration.
Configure the time-of-day clock for the CPU under the "Time of day" property. You can also
enable daylight saving time and specify the start and end times for daylight saving time. To
set the time-of-day clock, you must be online and in the "Online & diagnostics" view of the
CPU. Use the "Set time of day" function.