Every PLC has its own internal bit which can no be used by the programmer for making the program ,however these internal bits of plc shows the status of plc. Like there are bit defined for most of the functions like run mode , stop mode , time bit etc , These are the status bit which are helpful in determining the errors in plc and sometimes useful in plc program also.
Internal Memory Bit of a PLC :-
The internal auxiliary bits of plc has bits in this area which have preassigned functions. The value to these bits is written or changed by itself depending on the conditions. With the help of these internal bits Ladder programs can be simplified and controllability can be improved by effectively using the bits and words in this area. Some words or bits are set automatically by the system and others are set and manipulated by the user. The Auxiliary Area includes error flags set by self-diagnosis, initial settings, control bits, and status data. Words and bits in this area can be read and written from the program.
There are Internal Auxiliary bits like First Cycle Flag , First_Cycle, Step Flag P_Step, First Cycle Task Flag, P_First_Cycle_Task, Maximum Cycle Time P_Max_Cycle_Time, Present Cycle Time, P_Cycle_Time_Value,Cycle Time Too Long Flag, P_Cycle_Time_Error,Battery Error FlagP_Low_Battery
,Output OFF Bit and much more. These bits give the user a much advanced controllable features.
Also there is a particular area defined for maintaining the details of error log ,so that we can see the log of previous errors occurred in PLC and identify the problem. In addition to Internal Bits there are also Internal Data Words which are used for storing the time value of PLC and much more functions.
Also we will be discussing more about the time bits and words in Omron PLC , till then you can subscribe to get all latest updates regarding plc programming in yours inbox. Subscribe to Automation-Talk by Email.
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