In PLC, FRD instruction does the following operation 

• Programmable logic controllers or PLCs are digital computers used to perform control functions, usually for industrial applications.
• An instruction is a command that will cause a PLC to perform a certain predetermined operation.
• The instruction set for a particular PLC type lists the different types of instructions supported.
• The FRD command is an output command that is placed on the right side of the rung to convert a BCD value from a source to an integer value and place it into the destination when rung conditions are true.
• There are two values associated with this program, the Source and the Destination (Dest).
• The source and destination can be an address of a word (such as I:1, N7:0, T4:0).

An example is as shown: