Method, system, and apparatus for communicating using multiple controllers

1. A method of operating a control system that includes a plurality of controllers and at least one interface unit coupled to the plurality of controllers via a single network, said method comprising:

repeatedly transmitting a first interrupt to the at least one interface unit by a first controller of the plurality of controllers, the first interrupt transmitted at a first frequency;

receiving a first response at the first controller from the at least one interface unit responsive to the first interrupt;

repeatedly transmitting a second interrupt to the at least one interface unit by the second controller at the first frequency; and

receiving a second response at a second controller of the plurality of controllers from the at least one interface unit, the second response being aperiodic with respect to the first frequency;

wherein the first and second controllers operate simultaneously on the single network.

2. A method in accordance with claim 1 , wherein:

transmitting a first interrupt comprises transmitting the first interrupt including a data collection command; and

receiving a first response comprises receiving input data at the first controller from the at least one interface unit responsive to execution of the data collection command by the at least one interface unit.

3. A method in accordance with claim 1 , wherein transmitting a first interrupt comprises transmitting the first interrupt including a data storage command.

4. A method in accordance with claim 1 , wherein receiving a first response comprises receiving the first response at the first controller at the first frequency.

5. A method in accordance with claim 1 , further comprising pausing communication of the second response over the network from the at least one interface unit to enable processing of the first interrupt by the at least one interface unit.

6. A method in accordance with claim 1 , wherein the second response from the at least one interface unit is responsive to the second interrupt.

7. A method in accordance with claim 6 , wherein transmitting a second interrupt comprises repeatedly transmitting the second interrupt at a second frequency that is different than the first frequency.

8. A method in accordance with claim 1 , wherein the first controller includes a first shared memory and the second controller includes a second shared memory, said method further comprising accessing, by the first controller, a first portion of the first shared memory that is unavailable to the second controller.

9. A system comprising:

at least one interface unit comprising at least one input/output (I/O) module;

a first controller coupled to said at least one interface unit via a network, said first controller configured to:

repeatedly transmit a first interrupt to said at least one interface unit, the first interrupt transmitted at a first frequency; and

receive a first response from said at least one interface unit responsive to the first interrupt;

a second controller coupled to said at least one interface unit via said network, said second controller configured to:

repeatedly transmit a second interrupt to the at least one interface unit at the first frequency; and

receive a second response from said at least one interface unit, the second response being aperiodic with respect to the first frequency;

wherein the first and second controllers operate simultaneously on the single network.

10. A system in accordance with claim 9 , wherein said second controller is further configured to pause communication of the second response over said network from said at least one interface unit to enable processing of the first interrupt by said at least one interface unit.

11. A system in accordance with claim 9 , wherein the second response from said at least one interface unit is responsive to the second interrupt.

12. A system in accordance with claim 11 , wherein said second controller is configured to repeatedly transmit the second interrupt at a second frequency that is different than the first frequency.

13. A system in accordance with claim 9 , wherein said first controller comprises a first shared memory comprising a first portion that is unavailable to said second controller.

14. An interface unit for use with a control system, said interface unit coupled to a first controller and to a second controller via a single network, said interface unit comprising:

a processor configured to:

repeatedly receive a first interrupt from the first controller, the first interrupt received at a first frequency;

transmit a first response to the first controller responsive to the first interrupt;

repeatedly receive a second interrupt from the second controller at the first frequency;

transmit a second response to the second controller, the second response being aperiodic with respect to the first frequency; and

wherein the first and second controllers operate simultaneously on the single network.

15. An interface unit in accordance with claim 14 , wherein said processor is further configured to pause transmission of the second response upon receiving the first interrupt.

16. An interface unit in accordance with claim 14 , wherein said processor is further configured to:

transmit the second response to the second controller responsive to the second interrupt.

17. An interface unit in accordance with claim 16 , wherein at least one of the first interrupt and the second interrupt includes a data collection command, said processor further configured to:

execute the data collection command by acquiring input data from at least one input/output (I/O) module; and

transmit at least one of the first response and the second response including the input data.

18. An interface unit in accordance with claim 16 , wherein at least one of the first interrupt and the second interrupt includes a data storage command, said processor further configured to execute the data storage command by storing output data to at least one input/output module.