Method and apparatus for providing redundant I/O adapters in machine and process controllers

Apparatus for interfacing I/O modules having terminals accessible for attaching I/O wires to an I/O device on a controlled machine to a controller data I/O network in a machine or process control system having an industrial controller executing a stored program to control the machine or process, the apparatus comprising:

• a first communication adapter having a mounting surface and an electrical connection on a sidewall perpendicular to the mounting surface to communicate with the industrial controller through the controller data I/O network;
• a multiplexing module having
• a mounting surface,
• a first electrical connection on a first sidewall perpendicular to the mounting surface to mate with the electrical connection of the first communication adapter, and
• a second electrical connection on a second sidewall parallel to the first sidewall to allow the first communication adapter to communicate with the I/O modules, the multiplexing module including a serial bus connector;
• and
• a second communication adapter having
• a mounting surface,
• an electrical connection on a side wall perpendicular to the mounting surface and connected to a cable connecting to the serial bus connector of the multiplexing module and configured to provide an interface between the controller data I/O network and the machine or process,
• a network interface circuit configured to communicate with the industrial controller through the controller data I/O network;
• and
• an I/O data bus interface circuit for communicating with the I/O modules through an I/O data bus;
• wherein said second communication adapter and said first communication adapter receive output data from the controller through the controller data I/O network;
• wherein said second communication adapter and said first communication adapter each transmit output data through the I/O data bus when enabled as a primary communication adapter for the I/O modules,
• wherein in a redundant mode of operation, the multiplexing module monitors the network to determine that the first communication adapter has stopped communicating and that the second communication adapter should become the primary adapter for communicating with the I/O modules, and
• wherein the multiplexing module is connected to the I/O data bus in a position between the first communication adapter and the I/O modules.