User Manual

LOGO! functions
4.3 Special functions
LOGO!
Manual, 06/2014, A5E33039675
129
value to a high-precision timebase and makes continual corrections. The resultant maximum
timing inaccuracy is ±2 s/day.
4.3.3
Backup of the real-time clock
Because LOGO! backs up the internal real-time clock, it continues operation after a power
failure. The surrounding temperature influences the backup time. At a surrounding
temperature of 25°C, the typical backup time of a LOGO! 0BA8 is 20 days.
If there is a power outage of a LOGO! for more than 20 days, on restarting, the internal clock
is back in the status that it was in before the power outage.
4.3.4
Retentivity
You can set the switching states, counter and time values of many SF blocks (Page 131) to
be retentive. This means that LOGO! retains current data values after a power failure, and
that the block resumes operation at the break point. The timer is not reset, but resumes
operation until the time-to-go has expired.
To enable this response, however, the relevant functions must be set retentive. Two options
are available:
R: The data is retentive.
/
: Current data is not retentive (default). See the section in topic "Second circuit program
(Page 82)" on enabling and disabling retentivity.
The hours counter, weekly timer, yearly timer and PI controller are always retentive.
4.3.5
Parameter protection
In the parameter protection settings, you can determine whether or not you display and edit
the parameters in LOGO! parameter assignment mode. Two options are available:
+
: The parameter attribute permits read/write access in parameter assignment mode
(default).
-
: The parameter settings are read–/write–protected in parameter assignment mode, and you
can only edit them in programming mode. See the parameter protection mode example in
the Second circuit program (Page 82).
Note
Parameter protection covers only the "Set Parameter" window. If you embed variables of
protected special funct
ions in a message text, the variables are still editable from the
message text. To protect these variables, you must also activate the protection of the
message text.