Abstract: A method for encapsulating HTTP messages within a MODBUS message is described in the present invention. This MODBUS message can be encoded and sent using either MODBUS/TCP or serial MODBUS. Within MODBUS, the encapsulation is built using the MODBUS Encapsulation Interface (MEI). The HTTP message may contain HTML, XML, XHTML, or SGML.

Abstract: An interface circuit for use between an input circuit and an industrial automation system is disclosed. The industrial automation system includes an opto-coupler capable of being operably connected to the interface circuit. The interface circuit includes a first and second terminal, each terminal capable of being operably connected to the opto-coupler. A first current-source is operably connected to the first terminal and a second current-source is operably connected to the second terminal. A reference voltage is operably connected to the first current-source and the second current-source wherein the first and second current-source cooperate to provide a total input current in accordance with the operating characteristics of the industrial automation circuit.