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Programmable controller with I/O expansion module located in one of I/O module positions for communication with outside I/O modules

  • US 4,882,702 A
  • Filed: 05/16/1988
  • Issued: 11/21/1989
  • Est. Priority Date: 03/31/1986
  • Status: Expired due to Term
First Claim
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1. A method by which I/O status data is coupled under the control of an I/O scanning means between a first data table in a main memory and first and second groups of I/O modules that monitor and control I/O devices according to the I/O status data, wherein the first group of I/O modules is located in a first equipment rack having a backplane, and wherein the second group of I/O modules is located outside the first equipment rack, the method comprising:

  • connecting an I/O expansion module in any one of a plurality of I/O module positions in the first equipment rack corresponding to image table addresses existing within the first data table prior to I/O expansion, wherein the I/O expansion module has a second data table;

    coupling words of I/O data through the backplane and between the first data table and the I/O modules in the first equipment rack by decoding image table addresses within the first data table to sequentially enable each I/O module in turn to receive or transmit I/O status data according to whether the I/O module is an input module or an output module;

    coupling a multiword block of expansion I/O status data through the backplane and between the first data table and a second data table in the I/O expansion module, wherein the I/O expansion module is located at a single output address corresponding to a single image table address existing in the first data table prior of expansion; and

    coupling words of expansion I/O status between the block of expansion I/O status data in the second data table and the I/O modules outside the equipment rack via a serial data channel.

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