Provided by standard library.

MID returns a partial string from within a string.

Input STR is type STRING, LEN and POS are type INT, the return value of the function is type STRING.

MID (STR, LEN, POS) means: Retrieve LEN characters from the STR string beginning with the character at position POS.

Example in Function Block Diagram

Example in Structured Text

VarSTRING1 := MID ('SUSI',2,2);