Expansion system that automatically allows or blocks data from the PLC host using a clamping and decoding circuit to output clamping value

摘要

A serial-connection and parallel-communication fast interface for a PLC host and an expansion device includes a PLC host, at least one expansion device and shared bus comprising address lines, data lines, control lines and I/O addressing lines. The PLC host comprises an initial address output circuit and outputting a clamping value to the expander through an output addressing line. The expansion device includes a microprocessor, a memory unit and a clamping and decoding circuit such that the expansion device can automatically allocate the order thereof and output the clamping value through the addressing line. The expansion device can automatically allow or block the data from the PLC host. Therefore, the problem of overlong communication time for data access, the augmentation of expansion device and order limitation can be saved.