Abstract: In one aspect, the invention is a method for communicating with a device such as a programmable logic controller (PLC) or an I/O device. The method includes steps of: interconnecting the device to a personal computer (PC) running a web browser; and running an application on the PC that launches the web browser to an initial page and uploads a web browser applet or active x object from the device to the PC via the interconnection. The above-described embodiment combines PLC and/or I/O communications with the Internet's wide reach and ability to supply information, and does so with the “look and feel” of a PC-Internet interface without adding significantly to the overhead burden of these small devices.

Abstract: A method is provided for communicating among a plurality of programmable logic controllers (PLC's) coupled together on a common bus. A master PLC and a plurality of slave PLC's are coupled to the bus. An attach signal is transmitted by the master PLC to address and select the particular slave PLC to which the master PLC desires to transmit a message. The master PLC then transmits a mailbox signal including data and message length information regarding a next message if not all data from the master PLC and intended for the slave PLC could fit in the mailbox message. Additional next messages, each including data and next message length information, are sent by the master PLC to the selected slave PLC as necessary until all of the data intended for the selected slave PLC is transmitted by the master PLC.