Data extracting circuit for serial control apparatus

A data extracting circuit employable for a serial control apparatus including a main controller and a plurality of nodes each serving as an auxiliary controller, said main controller and said nodes being serially connected in a loop-shaped configuration or in a daisy chain-shaped configuration by a signal transmission line, said serial control apparatus being provided with at least one of time serial data including control data repeatedly periodically transmitted from said main controller to all nodes serially connected to said main controller via said signal transmission line and time serial data including sensing data repeatedly periodically transmitted from a specific one of said plurality of nodes to said main controller and all nodes serially connected to said specific node via said signal transmission line, said data extracting circuit being disposed in said main controller and in each of said plurality of nodes and serving to extract a data history with respect to said time serial data being repeatedly periodically transmitted, said data extracting circuit comprising:

• extracting means for extracting data in a specific time slot of said time series data,
• first latching means for latching said extracted data as new data each time said extracting means extracts data,
• second latching means for latching as old data the data latched by said first latching means in response to subsequent transmissions of said time series data,
• controlling means for controlling a terminal unit in response to the data latched by said second latching means,
• detecting means for detecting from said time series data presence or absence of an error and presence or absence of an error history representing that an error is present in said time series data, and
• inhibiting means for inhibiting data from being latched by said second latching means when at least one of the error and the error history is detected by said detecting means.