22
 
The  values  are  stored  also  in  case  of  power  failure  thanks  to  a 
rechargeable  back-up  battery.  After  charging,  the  battery  stores  data  for 
approx. 6 months 
 
1.7.2 Memory area “special marker SM” 
 
This  area  is  the  memory  which  contains  all  data  used  by  the  ladder 
program  to  interact  with the hardware resources  of  PL260.  Some  of  this 
data is initialized when starting the PLC with the default values described in 
the  table  below.  This  area  contains  all  data  related  to  analogue  inputs, 
trimmers, counts and set values of encoders, and also some bits controlled 
by the PLC for the ladder application as well as the settings for serial ports.  
The  table below includes  the  content  of each single  location  of  the area 
“Special markers”, giving the address for Modbus protocol and the type of 
operation  allowed  for  each  location  (R=reading,  W=writing, 
R/W=reading/writing).