Patent ID: 7246270

Claim:
A programmable controller comprising two communication units connected to a same network and a CPU unit that controls said two communication units; wherein said CPU has a checking function for checking, when power is switched on, whether or not same communication unit number has been set to different communication units of said programmable controller, and generating an error signal if same communication unit number has been set to different communication units of said programmable controller; wherein said CPU is prevented from executing said checking function regarding a specified communication unit number that is stored at a specified memory area whereby no error signal is generated when power is switched on although said specified communication unit number is set on two or more communication units of said programmable controller; wherein said two communication units are both identified by same identifying data including unit number and function such that one thereof operates in an active mode and the other thereof operates in a standby mode; wherein each of said communication units, when in said active mode, operates to carry out data exchanges with said CPU unit and other nodes connected to said network; wherein each of said communication units, when in said standby mode, in prevented from carrying out any data exchange with other nodes connected to said network; and wherein the communication unit in said standby mode is switched to said active mode and carries out the data exchange if the communication unit in said active mode fails.