State the function of PLC memory w.r.t. types, speed of execution.

State the function of PLC memory w.r.t. types, speed of execution.
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1 Answer

Answer :

PLC memory cab be divided into two major types:

1) System memory:

a) Executive Memory: The executive is a permanently stored collection of programs that are considered part of the system itself. These supervisory programs direct system activities, such as execution of the control program, communication with peripheral devices, and other system housekeeping activities.

b) Scratch Pad Memory: This is a temporary storage area used by the CPU to store a relatively small amount of data for interim calculations and control. The CPU stores data that is needed quickly in this memory area to avoid the longer access time involved with retrieving data from the main memory.

2) Application Memory:

a) Data Table Memory This area stores all data associated with the control program, such as timer/counter preset values and other stored constants and variables used by the control program or CPU. The data table also retains the status information of both the system inputs and the system outputs.

b) User Program Memory: This area provides storage for programmed instructions entered by the user. The user program area also stores the control program.

Executive memory is read only memory (ROM) type memory. Scratch pad, data table memory are random access memory (RAM) type memory. Program memory is flash ROM type memory. RAM memory is fastest amongst all type of memory. Flash ROM memory is faster than ROM memory. 
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