Abstract: A bus structure for interconnecting the modules of an industrial automation controller includes DATA lines and associated control lines that enable interface circuits on each module to transfer frames of data. The interface circuit includes a flow control circuit for managing resources within the receiving module, and thus controlling the flow of data over the backplane bus. As soon as a message begins to be received, the flow control circuit makes a determination as to the availability of resources within the module to successfully receive the data frame. If sufficient resources are not available, a busy indication is returned to the transmitting module, and the transmitting module then aborts the transmission.

Abstract: A bus structure for interconnecting the modules of an industrial automation controller includes DATA lines and associated control lines that enable interface circuits on each module to transfer frames of data. Modules connected to the bus structure support data transfers of differing widths and differing speeds, and interface circuits within each module automatically adapt to data width and speed differences between communicating modules. During a first bus cycle of each transfer, sending and receiving modules negotiate a bus width and clock speed to be used for the transfer by asserting their respective width and speed codes onto a set of wired-or status lines. After the first bus cycle, the status lines are then used for communicating alternate functions between the participating modules.