A PLC requires a programming terminal and programming soware for operation The programming terminal can be a dedicated terminal or a generic computer purchased anywhere.
The programming terminal is used for programming the PLC and monitoring the PLC’s operation.
It may also download a ladder logic program (the sending of a program from the programming terminal to the PLC) or upload a ladder logic program (the sending of a program from the PLC to the programming terminal).
The terminal uses programming sofiware for programming and “talking” to a PLC.