plc IO module programming

PLC programs are typically written in a special application on a personal computer, then downloaded by a direct-connection cable or over a network to the PLC. The program is stored in the plc IO module either in battery-backed-up RAM or some other non-volatile flash memory. Often, a single PLC can be programmed to replace thousands of relays.[7]
Under the IEC 61131-3 standard, plc analog output module can be programmed using standards-based programming languages. A graphical programming notation calledSequential Function Charts is available on certain programmable controllers. Initially most plc logic controller utilized Ladder Logic Diagram Programming, a model which emulated electromechanical control panel devices (such as the contact and coils of relays) which PLCs replaced. This model remains common today.