Abstract: A communication protocol employing dummy input and output values is used in communicating blocks of data between an industrial controller and its I/O modules while preventing premature use of partially transmitted data by the I/O modules yet without the need for special handshaking type circuitry or the continuous overhead of such handshaking protocols.

Abstract: A redundant controller employs two controller chassis having replaceable functional modules interconnected electrically within the chassis. System back up modules in the chassis coordinate the switching of control from a primary to a secondary chassis according to chassis redundancy state information of the chassis stored in the backup modules and module redundancy state information stored in the modules unique to the modules.

Abstract: In an industrial controller associated with independent I/O modules for exchanging signals between a controlled machine and the controller, a control program executed by the controller is associated with an I/O map identifying functionality of the independent I/O modules. At initialization of the controller, function keys are transmitted to the I/O modules, the latter which confirm that they are capable of the functions expected by the control program. The I/O modules may change their function according to the function keys and may accept functions not identical to those performed by the I/O module if the I/O module performs at greater functionality.