Abstract: An interface between a network communication card and an industrial controller allows rapid asynchronous buffering using two buffers and two associated registers for each data direction. A reading of the buffers is proceeded by an attempt to copy from the write designation register to the read designation register checking the equality of the register values and then reading from the buffer designated by their common value. Conclusion of the reading sets the write destination register to zero. Writing of the buffers is proceeded by a checking of the read designation register for zero value and then writing to other than the last buffer indicated by the write designation register. If the read designation register is non-zero, then the writing occurs to the opposite buffer of that in the read designation register. The write designation register is then updated to indicate the buffer written to.

Abstract: The density of I/O circuits on input and output modules in a programmable controller is doubled, while the number of optically coupled circuits is reduced, by transmitting data serially through one of the optically coupled circuits. Optically coupled circuits are also used for address and test signals and error-checking circuitry is provided to sense failures of the optically coupled circuits. The optically coupled circuits on each module are connected between two universal large scale integrated (LSI) circuits. The universal circuit can be operated on either the processor side or the machine side of either an input module or an output module by selecting a corresponding one of its four modes of operation. The multiplexing electronics on the input and output modules, aside from the optically coupled circuits, is integrated into just two components, and only one universal component is required for replacement of either of these two.