Programmable controller with module identification and diagnostic

Abstract

A programmable controller has a chassis which removably holds a plurality of functional modules. The chassis has a backplane with conductors and connectors that electrically connect the modules. These conductors carry module enable, read, and write control signals, as well as byte addresses and data. Another conductor carries a signal, which when true designates that files of data, as opposed to discrete bytes of data, are being exchanged over the backplane data conductors. Each module stores identification and diagnostic data as a number of individually addressable bytes. The identification and diagnostic data is obtained from a given module by sending an active module enable signal to it. At the same time the given module is sent inactive read and write signals and an active data file transfer signal. This combination of signals is used only to read the identification and diagnostic data and is not used to exchange other types of data with functional modules.