Different types of memory that are generally used in PLC s are as follows:
1. RAM:
2. ROM
A.)EPROM
B.)EEPROM
In PLC program instructions are stored in the memory. An internal communication high way also known as a bus system, carries information to and fro from the CPU, Memory and I/O units under the control of CPU Memory unit for storage of program. The user ladder logic program, is in the memory of PLC. The main program and other programs are necessary for operation of PLC.
The organization of the data and information in the memory is called memory map There are two types of memory used in PLC: Volatile and nonvolatile memory, in nonvolatile memories are generally used for storing user program so that the programs can return during power failure.
OR
Memory is classified into two types: 1. Storage memory: in storage memory store information on the status of i/o devices, pre assigned value of internal relay status and values for mathematical functions, this is called a data table or register table and stores information in two types: status and numbers,. Status is stored in the form of ON or OFF and nos are stored in the form of 1‟s and 0‟s is unique bit of memory. 2. User memory: in this memory, ladder logic programming is carried out and stored. User memory consists of program files or register table and holds the complete operation.