A method and apparatus for providing an active standby control system
includes the steps of providing a first and second programmable logic
controller (PLC), each controller having an operating state. Each
controller includes a network module board operably connected to a
network; a control unit, a remote I/O head; and, a hot standby module,
each hot standby module is operably connected together. PLC. This method
and apparatus can be used within a control system for monitoring input
devices and for controlling output devices which reside on the standard
communications network such as an Ethernet network, and the standard
communications protocol used therein can be TCP using Modbus.