Process control scanner apparatus

Claim 1

In a process control system including a computer wherein a plurality of test points are cyclically scanned so that binary changes in the states of the test points cause the computer to perform control operations, apparatus for reducing the scanning work load of the computer comprising: a plurality of memory units, each of said memory units being connected to one of said test points and beinG activated to store a binary representation when the associated test point changes state, said memory units being divided into groups wherein each group comprises several memory units; a data store, said data store including a plurality of registers, each of said registers being associated with a different one of said memory unit groups and each of said registers including a plurality of bit positions, each of said bit positions storing a binary representation related to the change of state of one of said test points; means for cyclically sampling said groups of memory units such that all the memory units of a group are sampled simultaneously; means for detecting a change of state of a given test point, as indicated by its associated memory unit within a given group; a first register; means responsive to said detecting means for transferring to said first register the binary representations stored by the given group of memory units wherein a change of state has been detected; a second register; means responsive to said cyclic sampling means and said detecting means for transferring to said second register the contents of the register of said data store which contains the binary representations associated with the given group of memory units whose binary representations have been transferred to said first register; logic means connected to said first and second registers for changing the binary significance of the binary representation stored in a given bit position of said second register only when the binary representation of the corresponding bit position of said first register has a given binary significance to form an updated group word; and means for transferring said updated group word back to the register of said data store associated with said given group of memory units.