It is common to find multiple PLCs within a single installation in modern industry. It can be different parts of the process that interact with each other or redundant systems that ensure continuity of service. Data exchange between PLCs has become simple to implement thanks to fieldbuses which allow a reliable real-time connection.
This is a companion discussion topic for the original entry at https://www.solisplc.com/tutorials/s7-plc-to-plc-communication-using-get-put-instructions-in-siemens-tia-portal